diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForIndexConflicts_Test.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForIndexConflicts_Test.java
new file mode 100644
index 0000000..2732377
--- /dev/null
+++ b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForIndexConflicts_Test.java
@@ -0,0 +1,227 @@
+/*
+ * Copyright (c) 2015 Google Inc.
+ *
+ * All rights reserved. This program and the accompanying materials are made available under the terms of the Eclipse
+ * Public License v1.0 which accompanies this distribution, and is available at
+ *
+ * http://www.eclipse.org/legal/epl-v10.html
+ */
+package com.google.eclipse.protobuf.validation;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.verifyZeroInteractions;
+import static com.google.eclipse.protobuf.junit.core.UnitTestModule.unitTestModule;
+import static com.google.eclipse.protobuf.junit.core.XtextRule.overrideRuntimeModuleWith;
+
+import java.util.List;
+
+import org.eclipse.emf.ecore.EObject;
+import org.eclipse.emf.ecore.EStructuralFeature;
+import org.eclipse.xtext.validation.ValidationMessageAcceptor;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+
+import com.google.eclipse.protobuf.junit.core.XtextRule;
+import com.google.eclipse.protobuf.protobuf.Group;
+import com.google.eclipse.protobuf.protobuf.IndexRange;
+import com.google.eclipse.protobuf.protobuf.Message;
+import com.google.eclipse.protobuf.protobuf.MessageField;
+import com.google.eclipse.protobuf.protobuf.ProtobufPackage;
+import com.google.inject.Inject;
+
+public class ProtobufJavaValidator_checkForIndexConflicts_Test {
+  @Rule public XtextRule xtext = overrideRuntimeModuleWith(unitTestModule());
+
+  @Inject private ProtobufJavaValidator validator;
+  private ValidationMessageAcceptor messageAcceptor;
+
+  @Before public void setUp() {
+    messageAcceptor = mock(ValidationMessageAcceptor.class);
+    validator.setMessageAcceptor(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Person {
+  //   reserved 10, 20 to 30;
+  //   reserved 10;
+  //   reserved 20;
+  //   reserved 25 to 26;
+  //   reserved 30 to 31;
+  // }
+  @Test public void should_error_on_conflict_between_reserved_and_reserved() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    List<IndexRange> indexRanges = xtext.findAll(IndexRange.class);
+    verifyError("Tag number 10 conflicts with reserved 10.", indexRanges.get(2));
+    verifyError("Tag number 20 conflicts with reserved 20 to 30.", indexRanges.get(3));
+    verifyError("Tag number range 25 to 26 conflicts with reserved 20 to 30.", indexRanges.get(4));
+    verifyError("Tag number range 30 to 31 conflicts with reserved 20 to 30.", indexRanges.get(5));
+    verifyNoMoreInteractions(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Person {
+  //   reserved 10, 20 to 30;
+  //   extensions 10, 15 to max;
+  // }
+  @Test public void should_error_on_conflict_between_reserved_and_extensions() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    List<IndexRange> indexRanges = xtext.findAll(IndexRange.class);
+    verifyError("Tag number 10 conflicts with reserved 10.", indexRanges.get(2));
+    verifyError("Tag number range 15 to max conflicts with reserved 20 to 30.", indexRanges.get(3));
+    verifyNoMoreInteractions(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Person {
+  //   reserved 10, 20 to 30;
+  //   optional bool foo = 10;
+  //   optional bool bar = 25;
+  //   group baz = 26 {
+  //     optional bool a = 27;
+  //   }
+  // }
+  @Test public void should_error_on_conflict_between_reserved_and_indexed_element() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    verifyError(
+        "Tag number 10 conflicts with reserved 10.",
+        xtext.findAll(MessageField.class).get(0),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 25 conflicts with reserved 20 to 30.",
+        xtext.findAll(MessageField.class).get(1),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 26 conflicts with reserved 20 to 30.",
+        xtext.findAll(Group.class).get(0),
+        ProtobufPackage.Literals.GROUP__INDEX);
+    verifyError(
+        "Tag number 27 conflicts with reserved 20 to 30.",
+        xtext.findAll(MessageField.class).get(2),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyNoMoreInteractions(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Person {
+  //   extensions 10, 20 to 30;
+  //   optional bool foo = 10;
+  //   optional bool bar = 25;
+  //   group baz = 26 {
+  //     optional bool a = 27;
+  //   }
+  // }
+  @Test public void should_error_on_conflict_between_extensions_and_indexed_element() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    verifyError(
+        "Tag number 10 conflicts with extensions 10.",
+        xtext.findAll(MessageField.class).get(0),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 25 conflicts with extensions 20 to 30.",
+        xtext.findAll(MessageField.class).get(1),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 26 conflicts with extensions 20 to 30.",
+        xtext.findAll(Group.class).get(0),
+        ProtobufPackage.Literals.GROUP__INDEX);
+    verifyError(
+        "Tag number 27 conflicts with extensions 20 to 30.",
+        xtext.findAll(MessageField.class).get(2),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyNoMoreInteractions(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Person {
+  //   optional bool foo1 = 1;
+  //   optional bool foo2 = 1;
+  //   repeated group foo3 = 1 {
+  //     optional bool foo4 = 1;
+  //   }
+  //   oneof choose_one {
+  //     optional bool foo5 = 1;
+  //   }
+  //
+  //   repeated group foo6 = 2 {
+  //     optional bool foo7 = 3;
+  //   }
+  //   optional bool foo8 = 2;
+  // }
+  @Test public void should_error_on_conflict_between_indexed_elements() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    verifyError(
+        "Tag number 1 conflicts with field \"foo1\".",
+        xtext.findAll(MessageField.class).get(1),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 1 conflicts with field \"foo1\".",
+        xtext.findAll(Group.class).get(0),
+        ProtobufPackage.Literals.GROUP__INDEX);
+    verifyError(
+        "Tag number 1 conflicts with field \"foo1\".",
+        xtext.findAll(MessageField.class).get(2),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 1 conflicts with field \"foo1\".",
+        xtext.findAll(MessageField.class).get(3),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyError(
+        "Tag number 2 conflicts with group \"foo6\".",
+        xtext.findAll(MessageField.class).get(5),
+        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
+    verifyNoMoreInteractions(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Car {
+  // }
+  //
+  // message Person {
+  //   extensions 10 to 20;
+  //   reserved 30 to 40;
+  //   optional bool foo = 50;
+  //   extend Car {
+  //     optional Person passenger_1 = 15;
+  //     optional Person passenger_2 = 35;
+  //     optional Person passenger_3 = 50;
+  //   }
+  // }
+  @Test public void should_not_find_conflicts_with_nested_type_extension_contents() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    verifyZeroInteractions(messageAcceptor);
+  }
+
+  // syntax = "proto2";
+  //
+  // message Person {
+  //   extensions 10 to 20;
+  //   reserved 30 to 40;
+  //   optional bool foo = 50;
+  //   message Car {
+  //     optional Person passenger_1 = 15;
+  //     optional Person passenger_2 = 35;
+  //     optional Person passenger_3 = 50;
+  //   }
+  // }
+  @Test public void should_not_find_conflicts_with_nested_message_contents() {
+    validator.checkForIndexConflicts(xtext.findFirst(Message.class));
+    verifyZeroInteractions(messageAcceptor);
+  }
+
+  private void verifyError(String message, EObject errorSource) {
+    verifyError(message, errorSource, null);
+  }
+
+  private void verifyError(String message, EObject errorSource, EStructuralFeature errorFeature) {
+    verify(messageAcceptor).acceptError(message, errorSource, errorFeature, -1, null);
+  }
+}
diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForIndexRangeConflicts_Test.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForIndexRangeConflicts_Test.java
deleted file mode 100644
index a29c8c3..0000000
--- a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForIndexRangeConflicts_Test.java
+++ /dev/null
@@ -1,142 +0,0 @@
-/*
- * Copyright (c) 2015 Google Inc.
- *
- * All rights reserved. This program and the accompanying materials are made available under the terms of the Eclipse
- * Public License v1.0 which accompanies this distribution, and is available at
- *
- * http://www.eclipse.org/legal/epl-v10.html
- */
-package com.google.eclipse.protobuf.validation;
-
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.verify;
-import static com.google.eclipse.protobuf.junit.core.UnitTestModule.unitTestModule;
-import static com.google.eclipse.protobuf.junit.core.XtextRule.overrideRuntimeModuleWith;
-
-import java.util.List;
-
-import org.eclipse.emf.ecore.EObject;
-import org.eclipse.emf.ecore.EStructuralFeature;
-import org.eclipse.xtext.validation.ValidationMessageAcceptor;
-import org.junit.Before;
-import org.junit.Rule;
-import org.junit.Test;
-
-import com.google.eclipse.protobuf.junit.core.XtextRule;
-import com.google.eclipse.protobuf.protobuf.Group;
-import com.google.eclipse.protobuf.protobuf.IndexRange;
-import com.google.eclipse.protobuf.protobuf.Message;
-import com.google.eclipse.protobuf.protobuf.MessageField;
-import com.google.eclipse.protobuf.protobuf.ProtobufPackage;
-import com.google.inject.Inject;
-
-public class ProtobufJavaValidator_checkForIndexRangeConflicts_Test {
-  @Rule public XtextRule xtext = overrideRuntimeModuleWith(unitTestModule());
-
-  @Inject private ProtobufJavaValidator validator;
-  private ValidationMessageAcceptor messageAcceptor;
-
-  @Before public void setUp() {
-    messageAcceptor = mock(ValidationMessageAcceptor.class);
-    validator.setMessageAcceptor(messageAcceptor);
-  }
-
-  // syntax = "proto2";
-  //
-  // message Person {
-  //   reserved 10, 20 to 30;
-  //   reserved 10;
-  //   reserved 20;
-  //   reserved 25 to 26;
-  //   reserved 30 to 31;
-  // }
-  @Test public void should_error_on_conflict_between_reserved_and_reserved() {
-    validator.checkForIndexRangeConflicts(xtext.findFirst(Message.class));
-    List<IndexRange> indexRanges = xtext.findAll(IndexRange.class);
-    verifyError("10 conflicts with reserved 10", indexRanges.get(2));
-    verifyError("20 conflicts with reserved 20 to 30", indexRanges.get(3));
-    verifyError("25 to 26 conflicts with reserved 20 to 30", indexRanges.get(4));
-    verifyError("30 to 31 conflicts with reserved 20 to 30", indexRanges.get(5));
-  }
-
-  // syntax = "proto2";
-  //
-  // message Person {
-  //   reserved 10, 20 to 30;
-  //   extensions 10, 15 to max;
-  // }
-  @Test public void should_error_on_conflict_between_reserved_and_extensions() {
-    validator.checkForIndexRangeConflicts(xtext.findFirst(Message.class));
-    List<IndexRange> indexRanges = xtext.findAll(IndexRange.class);
-    verifyError("10 conflicts with reserved 10", indexRanges.get(2));
-    verifyError("15 to max conflicts with reserved 20 to 30", indexRanges.get(3));
-  }
-
-  // syntax = "proto2";
-  //
-  // message Person {
-  //   reserved 10, 20 to 30;
-  //   optional bool foo = 10;
-  //   optional bool bar = 25;
-  //   group baz = 26 {
-  //     optional bool a = 27;
-  //   }
-  // }
-  @Test public void should_error_on_conflict_between_reserved_and_indexed_element() {
-    validator.checkForIndexRangeConflicts(xtext.findFirst(Message.class));
-    verifyError(
-        "10 conflicts with reserved 10",
-        xtext.findAll(MessageField.class).get(0),
-        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
-    verifyError(
-        "25 conflicts with reserved 20 to 30",
-        xtext.findAll(MessageField.class).get(1),
-        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
-    verifyError(
-        "26 conflicts with reserved 20 to 30",
-        xtext.findAll(Group.class).get(0),
-        ProtobufPackage.Literals.GROUP__INDEX);
-    verifyError(
-        "27 conflicts with reserved 20 to 30",
-        xtext.findAll(MessageField.class).get(2),
-        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
-  }
-
-  // syntax = "proto2";
-  //
-  // message Person {
-  //   extensions 10, 20 to 30;
-  //   optional bool foo = 10;
-  //   optional bool bar = 25;
-  //   group baz = 26 {
-  //     optional bool a = 27;
-  //   }
-  // }
-  @Test public void should_error_on_conflict_between_extensions_and_indexed_element() {
-    validator.checkForIndexRangeConflicts(xtext.findFirst(Message.class));
-    verifyError(
-        "10 conflicts with extensions 10",
-        xtext.findAll(MessageField.class).get(0),
-        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
-    verifyError(
-        "25 conflicts with extensions 20 to 30",
-        xtext.findAll(MessageField.class).get(1),
-        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
-    verifyError(
-        "26 conflicts with extensions 20 to 30",
-        xtext.findAll(Group.class).get(0),
-        ProtobufPackage.Literals.GROUP__INDEX);
-    verifyError(
-        "27 conflicts with extensions 20 to 30",
-        xtext.findAll(MessageField.class).get(2),
-        ProtobufPackage.Literals.MESSAGE_FIELD__INDEX);
-  }
-
-  private void verifyError(String message, EObject errorSource) {
-    verifyError(message, errorSource, null);
-  }
-
-  private void verifyError(String message, EObject errorSource, EStructuralFeature errorFeature) {
-    verify(messageAcceptor).acceptError(message, errorSource, errorFeature, -1, null);
-  }
-}
diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForReservedNameConflicts_Test.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForReservedNameConflicts_Test.java
index 307d127..074c5ea 100644
--- a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForReservedNameConflicts_Test.java
+++ b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkForReservedNameConflicts_Test.java
@@ -10,6 +10,7 @@
 
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyZeroInteractions;
 import static com.google.eclipse.protobuf.junit.core.UnitTestModule.unitTestModule;
 import static com.google.eclipse.protobuf.junit.core.XtextRule.overrideRuntimeModuleWith;
 
@@ -50,8 +51,8 @@
   @Test public void should_error_on_conflict_between_reserved_and_reserved() {
     validator.checkForReservedNameConflicts(xtext.findFirst(Message.class));
     List<StringLiteral> stringLiterals = xtext.findAll(StringLiteral.class);
-    verifyError("\"foo\" conflicts with reserved \"foo\"", stringLiterals.get(3));
-    verifyError("\"bar\" conflicts with reserved \"bar\"", stringLiterals.get(4));
+    verifyError("Name \"foo\" conflicts with reserved \"foo\".", stringLiterals.get(3));
+    verifyError("Name \"bar\" conflicts with reserved \"bar\".", stringLiterals.get(4));
   }
 
   // syntax = "proto2";
@@ -66,19 +67,37 @@
   @Test public void should_error_on_conflict_between_reserved_and_indexed_element() {
     validator.checkForReservedNameConflicts(xtext.findFirst(Message.class));
     verifyError(
-        "\"foo\" conflicts with reserved \"foo\"",
+        "Name \"foo\" conflicts with reserved \"foo\".",
         xtext.findAll(MessageField.class).get(0),
         ProtobufPackage.Literals.MESSAGE_FIELD__NAME);
     verifyError(
-        "\"bar\" conflicts with reserved \"bar\"",
+        "Name \"bar\" conflicts with reserved \"bar\".",
         xtext.findAll(Group.class).get(0),
         ProtobufPackage.Literals.COMPLEX_TYPE__NAME);
     verifyError(
-        "\"baz\" conflicts with reserved \"baz\"",
+        "Name \"baz\" conflicts with reserved \"baz\".",
         xtext.findAll(MessageField.class).get(1),
         ProtobufPackage.Literals.MESSAGE_FIELD__NAME);
   }
 
+  // syntax = "proto2";
+  //
+  // message Car {
+  // }
+  //
+  // message Person {
+  //   reserved "owner";
+  //   optional bool passenger = 1;
+  //   extend Car {
+  //     optional Person owner = 1;
+  //     repeated Person passenger = 2;
+  //   }
+  // }
+  @Test public void should_not_find_conflict_with_nested_extension() {
+    validator.checkForReservedNameConflicts(xtext.findFirst(Message.class));
+    verifyZeroInteractions(messageAcceptor);
+  }
+
   private void verifyError(String message, EObject errorSource) {
     verifyError(message, errorSource, null);
   }
diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkTagNumberIsUnique_Test.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkTagNumberIsUnique_Test.java
deleted file mode 100644
index c15c4e0..0000000
--- a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator_checkTagNumberIsUnique_Test.java
+++ /dev/null
@@ -1,71 +0,0 @@
-/*
- * Copyright (c) 2011 Google Inc.
- *
- * All rights reserved. This program and the accompanying materials are made available under the terms of the Eclipse
- * Public License v1.0 which accompanies this distribution, and is available at
- *
- * http://www.eclipse.org/legal/epl-v10.html
- */
-package com.google.eclipse.protobuf.validation;
-
-import static org.eclipse.xtext.validation.ValidationMessageAcceptor.INSIGNIFICANT_INDEX;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.verifyZeroInteractions;
-
-import static com.google.eclipse.protobuf.junit.core.UnitTestModule.unitTestModule;
-import static com.google.eclipse.protobuf.junit.core.XtextRule.overrideRuntimeModuleWith;
-import static com.google.eclipse.protobuf.protobuf.ProtobufPackage.Literals.MESSAGE_FIELD__INDEX;
-import static com.google.eclipse.protobuf.validation.ProtobufJavaValidator.INVALID_FIELD_TAG_NUMBER_ERROR;
-
-import org.eclipse.xtext.validation.ValidationMessageAcceptor;
-import org.junit.Before;
-import org.junit.Rule;
-import org.junit.Test;
-
-import com.google.eclipse.protobuf.junit.core.XtextRule;
-import com.google.eclipse.protobuf.protobuf.IndexedElement;
-import com.google.eclipse.protobuf.protobuf.MessageField;
-import com.google.inject.Inject;
-
-/**
- * Tests for <code>{@link ProtobufJavaValidator#checkTagNumberIsUnique(IndexedElement)}</code>
- *
- * @author alruiz@google.com (Alex Ruiz)
- */
-public class ProtobufJavaValidator_checkTagNumberIsUnique_Test {
-  @Rule public XtextRule xtext = overrideRuntimeModuleWith(unitTestModule());
-
-  @Inject private ProtobufJavaValidator validator;
-  private ValidationMessageAcceptor messageAcceptor;
-
-  @Before public void setUp() {
-    messageAcceptor = mock(ValidationMessageAcceptor.class);
-    validator.setMessageAcceptor(messageAcceptor);
-  }
-
-  // syntax = "proto2";
-  //
-  // message Person {
-  //   optional long id = 1;
-  //   optional string name = 1;
-  // }
-  @Test public void should_create_error_if_field_does_not_have_unique_tag_number() {
-    MessageField field = xtext.find("name", MessageField.class);
-    validator.checkTagNumberIsUnique(field);
-    String message = "Field number 1 has already been used in \"Person\" by field \"id\".";
-    verify(messageAcceptor).acceptError(message, field, MESSAGE_FIELD__INDEX, INSIGNIFICANT_INDEX, INVALID_FIELD_TAG_NUMBER_ERROR);
-  }
-
-  // syntax = "proto2";
-  //
-  // message Person {
-  //   optional long id = 1;
-  //   optional string name = 2;
-  // }
-  @Test public void should_not_create_error_if_field_has_unique_tag_number() {
-    MessageField field = xtext.find("name", MessageField.class);
-    validator.checkTagNumberIsUnique(field);
-    verifyZeroInteractions(messageAcceptor);
-  }
-}
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.java
index a54836c..85c2f9d 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.java
@@ -14,8 +14,11 @@
  * @author alruiz@google.com (Alex Ruiz)
  */
 public class Messages extends NLS {
-  public static String conflictsWithExtensions;
-  public static String conflictsWithReserved;
+  public static String conflictingExtensions;
+  public static String conflictingField;
+  public static String conflictingGroup;
+  public static String conflictingReservedName;
+  public static String conflictingReservedNumber;
   public static String expectedFieldName;
   public static String expectedFieldNumber;
   public static String expectedIdentifier;
@@ -25,7 +28,6 @@
   public static String expectedString;
   public static String expectedSyntaxIdentifier;
   public static String expectedTrueOrFalse;
-  public static String fieldNumberAlreadyUsed;
   public static String fieldNumbersMustBePositive;
   public static String importingUnsupportedSyntax;
   public static String importNotFound;
@@ -37,11 +39,14 @@
   public static String missingFieldNumber;
   public static String missingModifier;
   public static String multiplePackages;
+  public static String nameConflict;
   public static String oneofFieldWithModifier;
   public static String requiredInProto3;
   public static String reservedIndexAndName;
   public static String reservedToMax;
   public static String scopingError;
+  public static String tagNumberRangeConflict;
+  public static String tagNumberConflict;
   public static String unknownSyntax;
   public static String unrecognizedSyntaxIdentifier;
 
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties
index 7f46818..15aaf6a 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/Messages.properties
@@ -1,3 +1,8 @@
+conflictingExtensions = extensions %s
+conflictingField = field "%s"
+conflictingGroup = group "%s"
+conflictingReservedName = reserved "%s"
+conflictingReservedNumber = reserved %s
 expectedFieldName = Expected field name.
 expectedFieldNumber = Expected field number.
 expectedIdentifier = Expected identifier.
@@ -7,7 +12,6 @@
 expectedString = Expected string.
 expectedSyntaxIdentifier = Expected syntax identifier.
 expectedTrueOrFalse = Expected "true" or "false".
-fieldNumberAlreadyUsed = Field number %d has already been used in \"%s\" by field \"%s\".
 fieldNumbersMustBePositive = Field numbers must be positive integers.
 importingUnsupportedSyntax = Importing unsupported file (directly or indirectly.) This may cause errors related to unresolved references.
 importNotFound = Import \"%s\" was not found.
@@ -20,11 +24,12 @@
 missingModifier = Missing modifier: \"required\", \"optional\", or \"repeated\".
 oneofFieldWithModifier = Fields inside "oneof" cannot have a modifier.
 multiplePackages = Multiple package definitions.
-conflictsWithExtensions = %s conflicts with extensions %s
-conflictsWithReserved = %s conflicts with reserved %s
+nameConflict = Name "%s" conflicts with %s.
 requiredInProto3 = Required fields are not allowed in proto3.
 reservedIndexAndName = A reserved declaration may not include both numbers and names.
 reservedToMax = Reserved index range must have finite upper bound.
 scopingError = It may be caused by an imported non-proto2 file.
+tagNumberConflict = Tag number %s conflicts with %s.
+tagNumberRangeConflict = Tag number range %s conflicts with %s.
 unknownSyntax = Unknown syntax.  This parser only recognizes \"proto2\" or \"proto3\".
 unrecognizedSyntaxIdentifier = Unrecognized syntax identifier \"%s\".  This parser only recognizes \"proto2\" and \"proto3\".
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator.java
index 00b0350..d37b92d 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufJavaValidator.java
@@ -13,11 +13,8 @@
 import static com.google.eclipse.protobuf.protobuf.ProtobufPackage.Literals.MESSAGE_FIELD__MODIFIER;
 import static com.google.eclipse.protobuf.protobuf.ProtobufPackage.Literals.PACKAGE__NAME;
 import static com.google.eclipse.protobuf.protobuf.ProtobufPackage.Literals.SYNTAX__NAME;
-import static com.google.eclipse.protobuf.validation.Messages.conflictsWithExtensions;
-import static com.google.eclipse.protobuf.validation.Messages.conflictsWithReserved;
 import static com.google.eclipse.protobuf.validation.Messages.expectedFieldNumber;
 import static com.google.eclipse.protobuf.validation.Messages.expectedSyntaxIdentifier;
-import static com.google.eclipse.protobuf.validation.Messages.fieldNumberAlreadyUsed;
 import static com.google.eclipse.protobuf.validation.Messages.fieldNumbersMustBePositive;
 import static com.google.eclipse.protobuf.validation.Messages.invalidMapKeyType;
 import static com.google.eclipse.protobuf.validation.Messages.invalidMapValueType;
@@ -25,10 +22,18 @@
 import static com.google.eclipse.protobuf.validation.Messages.mapWithinTypeExtension;
 import static com.google.eclipse.protobuf.validation.Messages.missingModifier;
 import static com.google.eclipse.protobuf.validation.Messages.multiplePackages;
+import static com.google.eclipse.protobuf.validation.Messages.nameConflict;
 import static com.google.eclipse.protobuf.validation.Messages.oneofFieldWithModifier;
 import static com.google.eclipse.protobuf.validation.Messages.requiredInProto3;
 import static com.google.eclipse.protobuf.validation.Messages.reservedIndexAndName;
 import static com.google.eclipse.protobuf.validation.Messages.reservedToMax;
+import static com.google.eclipse.protobuf.validation.Messages.tagNumberRangeConflict;
+import static com.google.eclipse.protobuf.validation.Messages.tagNumberConflict;
+import static com.google.eclipse.protobuf.validation.Messages.conflictingExtensions;
+import static com.google.eclipse.protobuf.validation.Messages.conflictingField;
+import static com.google.eclipse.protobuf.validation.Messages.conflictingGroup;
+import static com.google.eclipse.protobuf.validation.Messages.conflictingReservedName;
+import static com.google.eclipse.protobuf.validation.Messages.conflictingReservedNumber;
 import static com.google.eclipse.protobuf.validation.Messages.unknownSyntax;
 import static com.google.eclipse.protobuf.validation.Messages.unrecognizedSyntaxIdentifier;
 import static java.lang.String.format;
@@ -36,10 +41,12 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
-import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 import com.google.common.collect.Iterables;
+import com.google.common.collect.LinkedHashMultimap;
+import com.google.common.collect.Multimap;
 import com.google.common.collect.Range;
 import com.google.eclipse.protobuf.model.util.IndexRanges;
 import com.google.eclipse.protobuf.model.util.IndexedElements;
@@ -48,12 +55,12 @@
 import com.google.eclipse.protobuf.model.util.Syntaxes;
 import com.google.eclipse.protobuf.naming.NameResolver;
 import com.google.eclipse.protobuf.protobuf.Extensions;
+import com.google.eclipse.protobuf.protobuf.Group;
 import com.google.eclipse.protobuf.protobuf.IndexRange;
 import com.google.eclipse.protobuf.protobuf.IndexedElement;
 import com.google.eclipse.protobuf.protobuf.MapType;
 import com.google.eclipse.protobuf.protobuf.MapTypeLink;
 import com.google.eclipse.protobuf.protobuf.Message;
-import com.google.eclipse.protobuf.protobuf.MessageElement;
 import com.google.eclipse.protobuf.protobuf.MessageField;
 import com.google.eclipse.protobuf.protobuf.ModifierEnum;
 import com.google.eclipse.protobuf.protobuf.OneOf;
@@ -71,12 +78,11 @@
 import com.google.eclipse.protobuf.protobuf.TypeLink;
 import com.google.inject.Inject;
 
+import org.eclipse.emf.common.util.TreeIterator;
 import org.eclipse.emf.ecore.EAttribute;
 import org.eclipse.emf.ecore.EObject;
 import org.eclipse.emf.ecore.EStructuralFeature;
 import org.eclipse.xtext.EcoreUtil2;
-import org.eclipse.xtext.naming.IQualifiedNameProvider;
-import org.eclipse.xtext.naming.QualifiedName;
 import org.eclipse.xtext.util.SimpleAttributeResolver;
 import org.eclipse.xtext.validation.Check;
 import org.eclipse.xtext.validation.ComposedChecks;
@@ -101,7 +107,6 @@
   @Inject private NameResolver nameResolver;
   @Inject private StringLiterals stringLiterals;
   @Inject private Protobufs protobufs;
-  @Inject private IQualifiedNameProvider qualifiedNameProvider;
   @Inject private Syntaxes syntaxes;
 
   @Check public void checkIsKnownSyntax(Protobuf protobuf) {
@@ -119,46 +124,67 @@
     error(msg, syntax, SYNTAX__NAME, SYNTAX_IS_NOT_KNOWN_ERROR);
   }
 
-  @Check public void checkForIndexRangeConflicts(Message message) {
-    Collection<Range<Long>> reservedRanges = new ArrayList<>();
-    for (Reserved reserved : getOwnedElements(Message.class, message, Reserved.class)) {
+  @Check public void checkForIndexConflicts(Message message) {
+    Multimap<EObject, Range<Long>> rangeUsages = LinkedHashMultimap.create();
+
+    for (Reserved reserved : getOwnedElements(message, Reserved.class)) {
       for (IndexRange indexRange : Iterables.filter(reserved.getReservations(), IndexRange.class)) {
         Range<Long> range = indexRanges.toLongRange(indexRange);
-        errorOnConflicts(range, reservedRanges, conflictsWithReserved, indexRange, null);
-        reservedRanges.add(range);
+        errorOnConflicts(range, rangeUsages, indexRange, null);
+        rangeUsages.put(reserved, range);
       }
     }
 
-    Collection<Range<Long>> extensionsRanges = new ArrayList<>();
-    for (Extensions extensions : getOwnedElements(Message.class, message, Extensions.class)) {
+    for (Extensions extensions : getOwnedElements(message, Extensions.class)) {
       for (IndexRange indexRange : extensions.getRanges()) {
         Range<Long> range = indexRanges.toLongRange(indexRange);
-        errorOnConflicts(range, reservedRanges, conflictsWithReserved, indexRange, null);
-        errorOnConflicts(range, extensionsRanges, conflictsWithExtensions, indexRange, null);
-        extensionsRanges.add(range);
+        errorOnConflicts(range, rangeUsages, indexRange, null);
+        rangeUsages.put(extensions, range);
       }
     }
 
-    for (IndexedElement element : getOwnedElements(Message.class, message, IndexedElement.class)) {
+    for (IndexedElement element : getOwnedElements(message, IndexedElement.class)) {
       long index = indexedElements.indexOf(element);
       Range<Long> range = Range.singleton(index);
-      EStructuralFeature indexFeature = indexedElements.indexFeatureOf(element);
-      errorOnConflicts(range, reservedRanges, conflictsWithReserved, element, indexFeature);
-      errorOnConflicts(range, extensionsRanges, conflictsWithExtensions, element, indexFeature);
+      EStructuralFeature feature = indexedElements.indexFeatureOf(element);
+      errorOnConflicts(range, rangeUsages, element, feature);
+      rangeUsages.put(element, range);
     }
   }
 
   private void errorOnConflicts(
       Range<Long> range,
-      Iterable<Range<Long>> existingRanges,
-      String errorTemplate,
+      Multimap<EObject, Range<Long>> rangeUsages,
       EObject errorSource,
       EStructuralFeature errorFeature) {
-    for (Range<Long> existingRange : existingRanges) {
-      if (range.isConnected(existingRange)) {
-        String message =
-            String.format(errorTemplate, rangeToString(range), rangeToString(existingRange));
+    for (Map.Entry<EObject, Range<Long>> rangeUsage : rangeUsages.entries()) {
+      Range<Long> usedRange = rangeUsage.getValue();
+      if (range.isConnected(usedRange)) {
+        EObject rangeUser = rangeUsage.getKey();
+
+        boolean rangeIsSingular =
+            range.hasUpperBound() && range.upperEndpoint() == range.lowerEndpoint();
+        String template = rangeIsSingular ? tagNumberConflict : tagNumberRangeConflict;
+
+        String rangeUserString;
+        String usedRangeString = rangeToString(usedRange);
+        if (rangeUser instanceof MessageField) {
+          rangeUserString =
+              String.format(conflictingField, nameResolver.nameOf(rangeUser), usedRangeString);
+        } else if (rangeUser instanceof Group) {
+          rangeUserString =
+              String.format(conflictingGroup, nameResolver.nameOf(rangeUser), usedRangeString);
+        } else if (rangeUser instanceof Reserved) {
+          rangeUserString = String.format(conflictingReservedNumber, usedRangeString);
+        } else {
+          rangeUserString = String.format(conflictingExtensions, usedRangeString);
+        }
+
+        String message = String.format(template, rangeToString(range), rangeUserString);
         error(message, errorSource, errorFeature);
+
+        // Don't report more than one error per element.
+        return;
       }
     }
   }
@@ -185,7 +211,7 @@
 
   @Check public void checkForReservedNameConflicts(Message message) {
     Set<String> reservedNames = new HashSet<>();
-    for (Reserved reserved : getOwnedElements(Message.class, message, Reserved.class)) {
+    for (Reserved reserved : getOwnedElements(message, Reserved.class)) {
       for (StringLiteral stringLiteral :
           Iterables.filter(reserved.getReservations(), StringLiteral.class)) {
         String name = stringLiterals.getCombinedString(stringLiteral);
@@ -194,7 +220,7 @@
       }
     }
 
-    for (IndexedElement element : getOwnedElements(Message.class, message, IndexedElement.class)) {
+    for (IndexedElement element : getOwnedElements(message, IndexedElement.class)) {
       String name = nameResolver.nameOf(element);
       if (name != null) {
         EAttribute nameAttribute = SimpleAttributeResolver.NAME_RESOLVER.getAttribute(element);
@@ -222,38 +248,36 @@
   private void reportReservedNameConflicts(
       String name, Set<String> reservedNames, EObject errorSource, EAttribute errorFeature) {
     if (reservedNames.contains(name)) {
-      String quotedName = '"' + name + '"';
-      String message = String.format(conflictsWithReserved, quotedName, quotedName);
+      String nameUser = String.format(conflictingReservedName, name);
+      String message = String.format(nameConflict, name, nameUser);
       error(message, errorSource, errorFeature);
     }
   }
 
-  private <E extends EObject, C extends EObject> Collection<E> getOwnedElements(
-      Class<C> containerType, C container, Class<E> elementType) {
-    List<E> allElements = EcoreUtil2.getAllContentsOfType(container, elementType);
-    List<E> ownedElements = new ArrayList<>(allElements.size());
-    for (E element : allElements) {
-      if (EcoreUtil2.getContainerOfType(element, containerType) == container) {
-        ownedElements.add(element);
+  /**
+   * Returns elements of the given type contained within the given message, except those contained
+   * within intervening Messages or TypeExtensions.
+   */
+  private static <E extends EObject> Collection<E> getOwnedElements(
+      Message container, Class<E> elementType) {
+    Collection<E> elements = new ArrayList<E>();
+
+    TreeIterator<EObject> elementsIterator = container.eAllContents();
+    while (elementsIterator.hasNext()) {
+      EObject element = elementsIterator.next();
+
+      if (elementType.isAssignableFrom(element.getClass())) {
+        @SuppressWarnings("unchecked")
+        E elementAsElementType = (E) element;
+        elements.add(elementAsElementType);
+      }
+
+      if (element instanceof Message || element instanceof TypeExtension) {
+        elementsIterator.prune();
       }
     }
-    return ownedElements;
-  }
 
-  @Check public void checkTagNumberIsUnique(IndexedElement e) {
-    if (isNameNull(e)) {
-      return; // we already show an error if name is null, no need to go further.
-    }
-
-    EObject container = e.eContainer();
-    if (container instanceof OneOf) {
-      container = container.eContainer();
-    }
-    if (container instanceof Message) {
-      Message message = (Message) container;
-      Iterable<MessageElement> elements = message.getElements();
-      checkTagNumberIsUnique(e, message, elements);
-    }
+    return elements;
   }
 
   @Check public void checkFieldModifiers(MessageField field) {
@@ -308,33 +332,6 @@
     return false;
   }
 
-  private boolean checkTagNumberIsUnique(IndexedElement e, EObject message,
-      Iterable<MessageElement> elements) {
-    long index = indexedElements.indexOf(e);
-
-    for (MessageElement element : elements) {
-      if (element instanceof OneOf) {
-        if (!checkTagNumberIsUnique(e, message, ((OneOf) element).getElements())) {
-          return false;
-        }
-      } else if (element instanceof IndexedElement) {
-        IndexedElement other = (IndexedElement) element;
-        if (other == e) {
-          return true;
-        }
-        if (indexedElements.indexOf(other) == index) {
-          QualifiedName messageName = qualifiedNameProvider.getFullyQualifiedName(message);
-          String msg = format(fieldNumberAlreadyUsed, index, messageName.toString(),
-              nameResolver.nameOf(other));
-          invalidTagNumberError(msg, e);
-          return false;
-        }
-      }
-    }
-
-    return true;
-  }
-
   @Check public void checkTagNumberIsGreaterThanZero(IndexedElement e) {
     if (isNameNull(e))
      {