diff --git a/com.google.eclipse.protobuf/schema/descriptor-source.exsd b/com.google.eclipse.protobuf/schema/descriptor-source.exsd
index 98b9724..94685c8 100644
--- a/com.google.eclipse.protobuf/schema/descriptor-source.exsd
+++ b/com.google.eclipse.protobuf/schema/descriptor-source.exsd
@@ -49,13 +49,13 @@
 
    <element name="source">
       <complexType>
-         <attribute name="class" type="string">
+         <attribute name="path" type="string" use="required">
             <annotation>
                <documentation>
                   Provides the contents of a descriptor.proto file.
                </documentation>
                <appInfo>
-                  <meta.attribute kind="java" basedOn=":com.google.eclipse.protobuf.scoping.IProtoDescriptorSource"/>
+                  <meta.attribute kind="resource"/>
                </appInfo>
             </annotation>
          </attribute>
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/IProtoDescriptorSource.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/IProtoDescriptorSource.java
deleted file mode 100644
index 319e45b..0000000
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/IProtoDescriptorSource.java
+++ /dev/null
@@ -1,37 +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.scoping;
-
-import com.google.inject.ImplementedBy;
-
-import org.eclipse.emf.common.util.URI;
-
-import java.io.*;
-
-/**
- * Provides the contents of <code>{@link ProtoDescriptor}</code>.
- * 
- * @author alruiz@google.com (Alex Ruiz)
- */
-@ImplementedBy(OssProtoDescriptorSource.class)
-public interface IProtoDescriptorSource {
-
-  /**
-   * Returns the URI of the resource containing the descriptor.
-   * @return the URI of the resource containing the descriptor.
-   */
-  URI uri();
-  
-  /**
-   * Returns the contents of the descriptor.
-   * @return the contents of the descriptor.
-   * @throws IOException if something goes wrong.
-   */
-  InputStream contents() throws IOException;
-}
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/OssProtoDescriptorSource.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/OssProtoDescriptorSource.java
deleted file mode 100644
index 01492b4..0000000
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/OssProtoDescriptorSource.java
+++ /dev/null
@@ -1,37 +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.scoping;
-
-import com.google.inject.Singleton;
-
-import org.eclipse.emf.common.util.URI;
-
-import java.io.*;
-import java.net.URL;
-
-/**
- * @author alruiz@google.com (Alex Ruiz)
- */
-@Singleton
-class OssProtoDescriptorSource implements IProtoDescriptorSource {
-
-  private static final String DESCRIPTOR_URL = "platform:/plugin/com.google.eclipse.protobuf/descriptor.proto";
-  
-  private static final URI DESCRIPTOR_URI = URI.createURI(DESCRIPTOR_URL);
-
-  public URI uri() {
-    return DESCRIPTOR_URI;
-  }
-
-  public InputStream contents() throws IOException {
-    URL url = new URL(DESCRIPTOR_URL);
-    return url.openConnection().getInputStream();
-  }
-
-}
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptor.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptor.java
index 31c4cf5..37706cf 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptor.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptor.java
@@ -21,11 +21,13 @@
 import com.google.eclipse.protobuf.util.ModelNodes;
 import com.google.inject.Inject;
 
+import org.eclipse.emf.common.util.URI;
 import org.eclipse.xtext.nodemodel.INode;
 import org.eclipse.xtext.parser.*;
 import org.eclipse.xtext.resource.XtextResource;
 
-import java.io.InputStreamReader;
+import java.io.*;
+import java.net.URL;
 import java.util.*;
 
 /**
@@ -51,13 +53,13 @@
 
   private final ModelNodes nodes;
 
-  @Inject public ProtoDescriptor(IParser parser, IProtoDescriptorSource source, ModelNodes nodes) {
+  @Inject public ProtoDescriptor(IParser parser, URI descriptorLocation, ModelNodes nodes) {
     this.nodes = nodes;
     addOptionTypes();
     InputStreamReader reader = null;
     try {
-      XtextResource resource = new XtextResource(source.uri());
-      reader = new InputStreamReader(source.contents(), "UTF-8");
+      XtextResource resource = new XtextResource(descriptorLocation);
+      reader = new InputStreamReader(contents(descriptorLocation), "UTF-8");
       IParseResult result = parser.parse(reader);
       root = (Protobuf) result.getRootASTElement();
       resource.getContents().add(root);
@@ -71,6 +73,17 @@
     }
   }
 
+  /**
+   * Returns the contents of the descriptor file at the given location.
+   * @param descriptorLocation the location of the descriptor file.
+   * @return the contents of the descriptor file.
+   * @throws IOException if something goes wrong.
+   */
+  protected InputStream contents(URI descriptorLocation) throws IOException {
+    URL url = new URL(descriptorLocation.toString());
+    return url.openConnection().getInputStream();
+  }
+
   private void addOptionTypes() {
     for (OptionType type : OptionType.values())
       optionsByType.put(type, new LinkedHashMap<String, Property>());
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptorProvider.java b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptorProvider.java
index f1d8ca5..8cc6b2b 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptorProvider.java
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/scoping/ProtoDescriptorProvider.java
@@ -8,11 +8,13 @@
  */
 package com.google.eclipse.protobuf.scoping;
 
+import static org.eclipse.xtext.util.Strings.isEmpty;
+
 import com.google.eclipse.protobuf.util.ModelNodes;
 import com.google.inject.*;
 
-import org.apache.log4j.Logger;
 import org.eclipse.core.runtime.*;
+import org.eclipse.emf.common.util.URI;
 import org.eclipse.xtext.parser.IParser;
 
 /**
@@ -25,10 +27,7 @@
 
   private static final String EXTENSION_ID = "com.google.eclipse.protobuf.descriptorSource";
 
-  private static Logger logger = Logger.getLogger(ProtoDescriptorProvider.class);
-  
   @Inject private IParser parser;
-  @Inject private IProtoDescriptorSource source;
   @Inject private ModelNodes nodes;
   @Inject private IExtensionRegistry registry;
 
@@ -39,24 +38,19 @@
   public ProtoDescriptor get() {
     synchronized (lock) {
       if (descriptor == null) {
-        IProtoDescriptorSource actualSource = sourceFromPlugin();
-        if (actualSource == null) actualSource = source;
-        descriptor = new ProtoDescriptor(parser, actualSource, nodes);
+        descriptor = new ProtoDescriptor(parser, descriptorLocation(), nodes);
       }
       return descriptor;
     }
   }
   
-  private IProtoDescriptorSource sourceFromPlugin() {
+  private URI descriptorLocation() {
     IConfigurationElement[] config = registry.getConfigurationElementsFor(EXTENSION_ID);
-    try {
-      for (IConfigurationElement e : config) {
-        Object extension = e.createExecutableExtension("class");
-        if (extension instanceof IProtoDescriptorSource) return (IProtoDescriptorSource) extension;
-      }
-    } catch (CoreException t) {
-      logger.fatal("Unable to instantiate extension elements", t);
+    for (IConfigurationElement e : config) {
+      String path = e.getAttribute("path");
+      if (isEmpty(path)) continue;
+      return URI.createURI("platform:/plugin/" + e.getContributor().getName() + "/" + path);
     }
-    return null;
+    return URI.createURI("platform:/plugin/com.google.eclipse.protobuf/descriptor.proto");
   }
 }