diff --git a/source/com/intellij/slicer/SliceUtil.java b/source/com/intellij/slicer/SliceUtil.java
index 02decf3999fa..5b7b234684d5 100644
--- a/source/com/intellij/slicer/SliceUtil.java
+++ b/source/com/intellij/slicer/SliceUtil.java
@@ -158,7 +158,9 @@ public class SliceUtil {
     for (final PsiMethod containingMethod : superMethods) {
       if (!MethodReferencesSearch.search(containingMethod).forEach(new Processor<PsiReference>() {
         public boolean process(final PsiReference reference) {
-          if (!processed.add(reference)) return true;
+          synchronized (processed) {
+            if (!processed.add(reference)) return true;
+          }
           PsiElement element = reference.getElement().getParent();
           if (!(element instanceof PsiCall)) return true;
           final PsiCall call = (PsiCall)element;
diff --git a/util/src/com/intellij/util/CommonProcessors.java b/util/src/com/intellij/util/CommonProcessors.java
index d85ed0e44c56..f188d0818181 100644
--- a/util/src/com/intellij/util/CommonProcessors.java
+++ b/util/src/com/intellij/util/CommonProcessors.java
@@ -43,7 +43,7 @@ public class CommonProcessors {
       return true;
     }
 
-    public <T> T[] toArray(T[] a) {
+    public T[] toArray(T[] a) {
       return myCollection.toArray(a);
     }
 
@@ -64,7 +64,7 @@ public class CommonProcessors {
       return true;
     }
 
-    public <T> T[] toArray(T[] a) {
+    public T[] toArray(T[] a) {
       return myCollection.toArray(a);
     }
 
@@ -85,7 +85,12 @@ public class CommonProcessors {
     }
 
     public boolean process(T t) {
-      return !processed.add(t) || myDelegate.process(t);
+      synchronized (processed) {
+        if (!processed.add(t)) {
+          return true;
+        }
+      }
+      return myDelegate.process(t);
     }
   }