diff --git a/com.google.eclipse.protobuf.integration.test/src/com/google/eclipse/protobuf/validation/ImportValidator_checkNonProto2Imports_Test.java b/com.google.eclipse.protobuf.integration.test/src/com/google/eclipse/protobuf/validation/ImportValidator_checkNonProto2Imports_Test.java
index 5b9a99b..f60840b 100644
--- a/com.google.eclipse.protobuf.integration.test/src/com/google/eclipse/protobuf/validation/ImportValidator_checkNonProto2Imports_Test.java
+++ b/com.google.eclipse.protobuf.integration.test/src/com/google/eclipse/protobuf/validation/ImportValidator_checkNonProto2Imports_Test.java
@@ -12,13 +12,13 @@
 import static com.google.eclipse.protobuf.junit.core.XtextRule.overrideRuntimeModuleWith;
 import static org.mockito.Mockito.*;
 
-import org.eclipse.xtext.validation.ValidationMessageAcceptor;
-import org.junit.*;
-
 import com.google.eclipse.protobuf.junit.core.XtextRule;
 import com.google.eclipse.protobuf.protobuf.Protobuf;
 import com.google.inject.Inject;
 
+import org.eclipse.xtext.validation.ValidationMessageAcceptor;
+import org.junit.*;
+
 /**
  * Tests for <code>{@link ImportValidator#checkNonProto2Imports(Protobuf)}</code>
  *
@@ -74,4 +74,12 @@
     validator.checkNonProto2Imports(xtext.root());
     verifyNoMoreInteractions(messageAcceptor);
   }
+
+  // syntax = "proto2";
+  //
+  // import "093651b0-5676-11e1-b86c-0800200c9a66.proto";
+  @Test public void should_not_add_warnings_if_imported_file_does_not_exist() {
+    validator.checkNonProto2Imports(xtext.root());
+    verifyNoMoreInteractions(messageAcceptor);
+  }
 }
diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/junit/core/IntegrationTestModule.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/junit/core/IntegrationTestModule.java
index beafd75..c714463 100644
--- a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/junit/core/IntegrationTestModule.java
+++ b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/junit/core/IntegrationTestModule.java
@@ -46,7 +46,7 @@
       }
       File file = protoFile(importUri);
       if (!file.exists()) {
-        throw new IllegalArgumentException("File: " + importUri + " does not exist.");
+        return; // file does not exist.
       }
       String resolvedUri = file.toURI().toString();
       anImport.setImportURI(resolvedUri);
diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic_constructor_Test.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic_constructor_Test.java
index dbcb6cb..3e03766 100644
--- a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic_constructor_Test.java
+++ b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic_constructor_Test.java
@@ -35,7 +35,7 @@
     new ProtobufDiagnostic("1000", null, "message", node);
   }
 
-  @Test(expected = NullPointerException.class)
+  @Test(expected = IllegalArgumentException.class)
   public void should_throw_exception_if_data_contains_nulls() {
     new ProtobufDiagnostic("1000", new String[] { null }, "message", node);
   }
diff --git a/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/model/util/Imports_resolvedUriOf_Test.java b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/model/util/Imports_resolvedUriOf_Test.java
new file mode 100644
index 0000000..f94fb74
--- /dev/null
+++ b/com.google.eclipse.protobuf.test/src/com/google/eclipse/protobuf/model/util/Imports_resolvedUriOf_Test.java
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2012 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.model.util;
+
+import static com.google.eclipse.protobuf.junit.core.UnitTestModule.unitTestModule;
+import static com.google.eclipse.protobuf.junit.core.XtextRule.overrideRuntimeModuleWith;
+import static org.hamcrest.core.IsEqual.equalTo;
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
+
+import com.google.eclipse.protobuf.junit.core.*;
+import com.google.eclipse.protobuf.protobuf.Import;
+import com.google.inject.Inject;
+
+import org.eclipse.emf.common.util.URI;
+import org.eclipse.xtext.scoping.impl.ImportUriResolver;
+import org.junit.*;
+
+/**
+ * Tests for <code>{@link Imports#resolvedUriOf(Import)}</code>
+ *
+ * @author alruiz@google.com (Alex Ruiz)
+ */
+public class Imports_resolvedUriOf_Test {
+  @Rule public XtextRule xtext = overrideRuntimeModuleWith(unitTestModule(), new TestModule());
+
+  @Inject private ImportUriResolver uriResolver;
+  @Inject private Imports imports;
+
+  private Import anImport;
+
+  @Before public void setUp() {
+    anImport = mock(Import.class);
+  }
+
+  @Test public void should_return_resolved_URI() {
+    when(uriResolver.apply(anImport)).thenReturn("file:/protos/test.proto");
+    URI uri = imports.resolvedUriOf(anImport);
+    assertThat(uri.path(), equalTo("/protos/test.proto"));
+  }
+
+  @Test public void should_return_null_if_URI_cannot_be_resolved() {
+    when(uriResolver.apply(anImport)).thenReturn(null);
+    URI uri = imports.resolvedUriOf(anImport);
+    assertNull(uri);
+  }
+
+  private static class TestModule extends AbstractTestModule {
+    @Override protected void configure() {
+      mockAndBind(ImportUriResolver.class);
+    }
+  }
+}
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic.java
index 80a5387..d6591a5 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/linking/ProtobufDiagnostic.java
@@ -12,11 +12,11 @@
 import static java.util.Arrays.copyOf;
 import static org.eclipse.xtext.util.Arrays.contains;
 
+import com.google.common.base.Objects;
+
 import org.eclipse.xtext.diagnostics.*;
 import org.eclipse.xtext.nodemodel.INode;
 
-import com.google.common.base.Objects;
-
 /**
  * <code>{@link Diagnostic}</code> that supports appending text to its message.
  *
@@ -29,9 +29,14 @@
   private final INode node;
 
   public ProtobufDiagnostic(String code, String[] data, String message, INode node) {
-    validate(data);
+    if (data == null) {
+      throw new NullPointerException("The given array should not be null");
+    }
+    if (contains(data, null)) {
+      throw new IllegalArgumentException("The given array should not contain null elements");
+    }
     if (node == null) {
-      throw new NullPointerException("node should not be null");
+      throw new NullPointerException("The given node should not be null");
     }
     this.code = code;
     this.data = copyOf(data, data.length);
@@ -40,15 +45,6 @@
     this.node = node;
   }
 
-  private static void validate(String[] data) {
-    if (data == null) {
-      throw new NullPointerException("data should not be a null array");
-    }
-    if (contains(data, null)) {
-      throw new NullPointerException("data should not contain null");
-    }
-  }
-
   @Override public String getCode() {
     return code;
   }
@@ -66,7 +62,7 @@
   }
 
   /**
-   * Appends the given text to the message of this diagnostic.
+   * Appends the given text to this diagnostic's message.
    * @param s the text to append.
    */
   public void appendToMessage(String s) {
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/model/util/Imports.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/model/util/Imports.java
index 408118c..d308b3f 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/model/util/Imports.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/model/util/Imports.java
@@ -12,16 +12,16 @@
 import static com.google.eclipse.protobuf.util.Strings.*;
 import static org.eclipse.xtext.util.Strings.*;
 
-import org.eclipse.emf.common.util.URI;
-import org.eclipse.emf.ecore.resource.*;
-import org.eclipse.xtext.nodemodel.INode;
-import org.eclipse.xtext.scoping.impl.ImportUriResolver;
-
 import com.google.eclipse.protobuf.protobuf.Import;
 import com.google.eclipse.protobuf.resource.ResourceSets;
 import com.google.eclipse.protobuf.scoping.ProtoDescriptorProvider;
 import com.google.inject.Inject;
 
+import org.eclipse.emf.common.util.URI;
+import org.eclipse.emf.ecore.resource.*;
+import org.eclipse.xtext.nodemodel.INode;
+import org.eclipse.xtext.scoping.impl.ImportUriResolver;
+
 /**
  * Utility methods related to imports.
  *
@@ -90,10 +90,10 @@
    * @return {@code true} if the URI of the given {@code Import} has been resolved, {@code false} otherwise.
    */
   public boolean isResolved(Import anImport) {
-    String importUri = anImport.getImportURI();
-    if (!isEmpty(importUri)) {
-      URI uri = URI.createURI(importUri);
-      if (!isEmpty(uri.scheme())) {
+    String uriAsText = anImport.getImportURI();
+    if (!isEmpty(uriAsText)) {
+      URI uri = URI.createURI(uriAsText);
+      if (isResolved(uri)) {
         return true;
       }
     }
@@ -122,6 +122,14 @@
    */
   public URI resolvedUriOf(Import anImport) {
     String resolvedUri = uriResolver.apply(anImport);
-    return (isEmpty(resolvedUri)) ? null : URI.createURI(resolvedUri);
+    if (isEmpty(resolvedUri)) {
+      return null;
+    }
+    URI uri = URI.createURI(resolvedUri);
+    return (isResolved(uri)) ? uri : null;
+  }
+
+  private boolean isResolved(URI uri) {
+    return !isEmpty(uri.scheme());
   }
 }
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ImportValidator.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ImportValidator.java
index d852659..878ae52 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ImportValidator.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ImportValidator.java
@@ -15,16 +15,16 @@
 import static java.lang.String.format;
 import static org.eclipse.xtext.util.Tuples.pair;
 
-import java.util.*;
+import com.google.eclipse.protobuf.model.util.*;
+import com.google.eclipse.protobuf.protobuf.*;
+import com.google.inject.Inject;
 
 import org.eclipse.emf.ecore.resource.Resource;
 import org.eclipse.xtext.scoping.impl.ImportUriResolver;
 import org.eclipse.xtext.util.Pair;
 import org.eclipse.xtext.validation.*;
 
-import com.google.eclipse.protobuf.model.util.*;
-import com.google.eclipse.protobuf.protobuf.*;
-import com.google.inject.Inject;
+import java.util.*;
 
 /**
  * Verifies that "imports" contain correct values.
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufResourceValidator.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufResourceValidator.java
index f161e5a..648bc90 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufResourceValidator.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/validation/ProtobufResourceValidator.java
@@ -18,7 +18,7 @@
 import static org.eclipse.xtext.validation.CheckType.FAST;
 import static org.eclipse.xtext.validation.impl.ConcreteSyntaxEValidator.DISABLE_CONCRETE_SYNTAX_EVALIDATOR;
 
-import java.util.*;
+import com.google.eclipse.protobuf.linking.ProtobufDiagnostic;
 
 import org.apache.log4j.Logger;
 import org.eclipse.emf.common.util.Diagnostic;
@@ -29,7 +29,7 @@
 import org.eclipse.xtext.util.*;
 import org.eclipse.xtext.validation.*;
 
-import com.google.eclipse.protobuf.linking.ProtobufDiagnostic;
+import java.util.*;
 
 /**
  * Adds support for converting scoping errors into warnings if non-proto2 files are imported.
@@ -48,51 +48,18 @@
     List<Issue> result = newArrayListWithExpectedSize(resource.getErrors().size() + resource.getWarnings().size());
     try {
       IAcceptor<Issue> acceptor = createAcceptor(result);
-      boolean hasNonProto2Import = false;
-      for (EObject element : resource.getContents()) {
-        try {
-          if (monitor.isCanceled()) {
-            return null;
-          }
-          Diagnostic diagnostic = getDiagnostician().validate(element, validationOptions(resource, mode, monitor));
-          if (!diagnostic.getChildren().isEmpty()) {
-            for (Diagnostic child : diagnostic.getChildren()) {
-              if (importingNonProto2.equals(child.getMessage())) {
-                hasNonProto2Import = true;
-              }
-              issueFromEValidatorDiagnostic(child, acceptor);
-            }
-          } else {
-            issueFromEValidatorDiagnostic(diagnostic, acceptor);
-          }
-        } catch (RuntimeException e) {
-          log.error(e.getMessage(), e);
-        }
+      Status status = delegateValidationToDiagnostician(resource, mode, monitor, acceptor);
+      if (status.isCanceled()) {
+        return null;
       }
       if (mode.shouldCheck(FAST)) {
-        for (Resource.Diagnostic error : resource.getErrors()) {
-          if (monitor.isCanceled()) {
-            return null;
-          }
-          Severity severity = ERROR;
-          if (hasNonProto2Import && isUnresolveReferenceError(error)) {
-            severity = WARNING;
-            ProtobufDiagnostic d = (ProtobufDiagnostic) error;
-            if (!d.getMessage().endsWith(scopingError)) {
-              if (!d.getMessage().endsWith(".")) {
-                d.appendToMessage(".");
-              }
-              d.appendToMessage(" ");
-              d.appendToMessage(scopingError);
-            }
-          }
-          issueFromXtextResourceDiagnostic(error, severity, acceptor);
+        status = createErrors(resource, status.hasProto1Imports(), acceptor, monitor);
+        if (status.isCanceled()) {
+          return null;
         }
-        for (Resource.Diagnostic warning : resource.getWarnings()) {
-          if (monitor.isCanceled()) {
-            return null;
-          }
-          issueFromXtextResourceDiagnostic(warning, WARNING, acceptor);
+        status = createWarnings(resource, acceptor, monitor);
+        if (status.isCanceled()) {
+          return null;
         }
       }
     } catch (RuntimeException e) {
@@ -101,6 +68,21 @@
     return result;
   }
 
+  private Status delegateValidationToDiagnostician(Resource resource, CheckMode mode,
+      CancelIndicator monitor, IAcceptor<Issue> acceptor) {
+    Status hasNonProto2Import = Status.OK;
+    for (EObject element : resource.getContents()) {
+      if (monitor.isCanceled()) {
+        return Status.CANCELED;
+      }
+      Diagnostic diagnostic = getDiagnostician().validate(element, validationOptions(resource, mode, monitor));
+      if (convertIssuesToMarkers(acceptor, diagnostic) == Status.PROTO1_IMPORTS_FOUND) {
+        hasNonProto2Import = Status.PROTO1_IMPORTS_FOUND;
+      }
+    }
+    return hasNonProto2Import;
+  }
+
   private Map<Object, Object> validationOptions(Resource resource, CheckMode mode, CancelIndicator monitor) {
     Map<Object, Object> options = newHashMap();
     options.put(KEY, mode);
@@ -113,14 +95,76 @@
     return options;
   }
 
-  private boolean isUnresolveReferenceError(Resource.Diagnostic error) {
+  private Status convertIssuesToMarkers(IAcceptor<Issue> acceptor, Diagnostic diagnostic) {
+    Status hasNonProto2Import = Status.OK;
+    if (diagnostic.getChildren().isEmpty()) {
+      issueFromEValidatorDiagnostic(diagnostic, acceptor);
+      return hasNonProto2Import;
+    }
+    for (Diagnostic child : diagnostic.getChildren()) {
+      if (importingNonProto2.equals(child.getMessage())) {
+        hasNonProto2Import = Status.PROTO1_IMPORTS_FOUND;
+      }
+      issueFromEValidatorDiagnostic(child, acceptor);
+    }
+    return hasNonProto2Import;
+  }
+
+  private Status createErrors(Resource resource, boolean proto1ImportsFound, IAcceptor<Issue> acceptor,
+      CancelIndicator monitor) {
+    for (Resource.Diagnostic error : resource.getErrors()) {
+      if (monitor.isCanceled()) {
+        return Status.CANCELED;
+      }
+      Severity severity = ERROR;
+      if (proto1ImportsFound && isUnresolvedReferenceError(error)) {
+        severity = WARNING;
+        ProtobufDiagnostic d = (ProtobufDiagnostic) error;
+        String message = d.getMessage();
+        if (message.endsWith(scopingError)) {
+          continue;
+        }
+        if (!message.endsWith(".")) {
+          d.appendToMessage(".");
+        }
+        d.appendToMessage(" ");
+        d.appendToMessage(scopingError);
+      }
+      issueFromXtextResourceDiagnostic(error, severity, acceptor);
+    }
+    return Status.OK;
+  }
+
+  private boolean isUnresolvedReferenceError(Resource.Diagnostic error) {
     if (!(error instanceof ProtobufDiagnostic)) {
       return false;
     }
     ProtobufDiagnostic d = (ProtobufDiagnostic) error;
-    if (!"org.eclipse.xtext.diagnostics.Diagnostic.Linking".equals(d.getCode())) {
-      return false;
+    if ("org.eclipse.xtext.diagnostics.Diagnostic.Linking".equals(d.getCode())) {
+      return error.getMessage().startsWith("Couldn't resolve");
     }
-    return error.getMessage().startsWith("Couldn't resolve");
+    return false;
+  }
+
+  private Status createWarnings(Resource resource, IAcceptor<Issue> acceptor, CancelIndicator monitor) {
+    for (Resource.Diagnostic warning : resource.getWarnings()) {
+      if (monitor.isCanceled()) {
+        return Status.CANCELED;
+      }
+      issueFromXtextResourceDiagnostic(warning, WARNING, acceptor);
+    }
+    return Status.OK;
+  }
+
+  private static enum Status {
+    OK, CANCELED, PROTO1_IMPORTS_FOUND;
+
+    boolean hasProto1Imports() {
+      return (this == PROTO1_IMPORTS_FOUND);
+    }
+
+    boolean isCanceled() {
+      return (this == CANCELED);
+    }
   }
 }
\ No newline at end of file