diff --git a/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesIndex.java b/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesIndex.java
index fc104ec480fb..bbceb2d24059 100644
--- a/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesIndex.java
+++ b/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesIndex.java
@@ -54,7 +54,8 @@ import java.util.Map;
 public class DuplicatesIndex extends FileBasedIndexExtension<Integer, TIntArrayList> implements PsiDependentIndex {
   static boolean ourEnabled = SystemProperties.getBooleanProperty("idea.enable.duplicates.online.calculation",
                                                                   isEnabledByDefault());
-  static boolean ourEnabledLightProfiles = true;
+  static final boolean ourEnabledLightProfiles = true;
+  private static boolean ourEnabledOldProfiles = false;
 
   private static boolean isEnabledByDefault() {
     Application application = ApplicationManager.getApplication();
@@ -62,12 +63,15 @@ public class DuplicatesIndex extends FileBasedIndexExtension<Integer, TIntArrayL
   }
 
   @NonNls public static final ID<Integer, TIntArrayList> NAME = ID.create("DuplicatesIndex");
-  private static final int myBaseVersion = 15;
+  private static final int myBaseVersion = 16;
 
   private final FileBasedIndex.InputFilter myInputFilter = new FileBasedIndex.InputFilter() {
     @Override
     public boolean acceptInput(@NotNull final VirtualFile file) {
-      return ourEnabled && findDuplicatesProfile(file.getFileType()) != null;
+      return ourEnabled &&
+             findDuplicatesProfile(file.getFileType()) != null &&
+             file.isInLocalFileSystem() // skip library sources
+        ;
     }
   };
 
@@ -151,12 +155,14 @@ public class DuplicatesIndex extends FileBasedIndexExtension<Integer, TIntArrayL
     if (!(fileType instanceof LanguageFileType)) return null;
     Language language = ((LanguageFileType)fileType).getLanguage();
     DuplicatesProfile profile = DuplicatesProfile.findProfileForLanguage(language);
-    return profile != null && (profile.supportDuplicatesIndex() || profile instanceof LightDuplicateProfile) ? profile : null;
+    return profile != null &&
+           (ourEnabledOldProfiles && profile.supportDuplicatesIndex() ||
+            profile instanceof LightDuplicateProfile) ? profile : null;
   }
 
   @Override
   public int getVersion() {
-    return myBaseVersion + (ourEnabled ? 0xFF : 0) + (ourEnabledLightProfiles ? 0x7F : 0);
+    return myBaseVersion + (ourEnabled ? 0xFF : 0) + (ourEnabledLightProfiles ? 0x7F : 0) + (ourEnabledOldProfiles ? 0x21 : 0);
   }
 
   @Override
@@ -237,6 +243,13 @@ public class DuplicatesIndex extends FileBasedIndexExtension<Integer, TIntArrayL
     return old;
   }
 
+  @TestOnly
+  public static boolean setEnabledOldProfiles(boolean value) {
+    boolean old = ourEnabledOldProfiles;
+    ourEnabledOldProfiles = value;
+    return old;
+  }
+
   @Override
   public boolean hasSnapshotMapping() {
     return true;
diff --git a/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesInspectionBase.java b/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesInspectionBase.java
index 4fe5fd6c4fd7..29fcee2abddc 100644
--- a/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesInspectionBase.java
+++ b/platform/duplicates-analysis/src/com/intellij/dupLocator/index/DuplicatesInspectionBase.java
@@ -48,8 +48,10 @@ public class DuplicatesInspectionBase extends LocalInspectionTool {
     final Ref<DuplicatedCodeProcessor> myProcessorRef = new Ref<DuplicatedCodeProcessor>();
 
     final FileASTNode node = psiFile.getNode();
-    if (profile instanceof LightDuplicateProfile && node.getElementType() instanceof ILightStubFileElementType &&
-        DuplicatesIndex.ourEnabledLightProfiles) {
+    boolean usingLightProfile = profile instanceof LightDuplicateProfile &&
+                                node.getElementType() instanceof ILightStubFileElementType &&
+                                DuplicatesIndex.ourEnabledLightProfiles;
+    if (usingLightProfile) {
       LighterAST ast = node.getLighterAST();
       assert ast != null;
       ((LightDuplicateProfile)profile).process(ast, new LightDuplicateProfile.Callback() {
@@ -81,6 +83,11 @@ public class DuplicatesInspectionBase extends LocalInspectionTool {
             protected int getEndOffset(LighterASTNode node) {
               return node.getEndOffset();
             }
+
+            @Override
+            protected boolean isLightProfile() {
+              return true;
+            }
           }
           if (myProcessor == null) {
             myProcessor = new LightDuplicatedCodeProcessor(virtualFile, psiFile.getProject());
@@ -136,6 +143,11 @@ public class DuplicatesInspectionBase extends LocalInspectionTool {
             protected int getEndOffset(PsiFragment node) {
               return node.getEndOffset();
             }
+
+            @Override
+            protected boolean isLightProfile() {
+              return false;
+            }
           }
           if (myProcessor == null) {
             myProcessor = new OldDuplicatedCodeProcessor(virtualFile, psiFile.getProject());
@@ -154,7 +166,7 @@ public class DuplicatesInspectionBase extends LocalInspectionTool {
       for(Map.Entry<Integer, TextRange> entry:processor.reportedRanges.entrySet()) {
         final Integer offset = entry.getKey();
         // todo 3 statements constant
-        if (processor.fragmentSize.get(offset) < MIN_FRAGMENT_SIZE) continue;
+        if (!usingLightProfile && processor.fragmentSize.get(offset) < MIN_FRAGMENT_SIZE) continue;
         final VirtualFile file = processor.reportedFiles.get(offset);
         String message = "Found duplicated code in " + file.getPath();
 
@@ -244,7 +256,7 @@ public class DuplicatesInspectionBase extends LocalInspectionTool {
         reportedOffsetInOtherFiles.put(fragmentStartOffsetInteger, value);
         reportedPsi.put(fragmentStartOffsetInteger, target);
         fragmentSize.put(fragmentStartOffsetInteger, newFragmentSize);
-        if (newFragmentSize >= MIN_FRAGMENT_SIZE) fragmentHash.put(fragmentStartOffsetInteger, myHash);
+        if (newFragmentSize >= MIN_FRAGMENT_SIZE || isLightProfile()) fragmentHash.put(fragmentStartOffsetInteger, myHash);
         return false;
       }
       return true;
@@ -255,5 +267,6 @@ public class DuplicatesInspectionBase extends LocalInspectionTool {
 
     protected abstract int getStartOffset(T node);
     protected abstract int getEndOffset(T node);
+    protected abstract boolean isLightProfile();
   }
 }