diff --git a/platform/core-impl/src/com/intellij/openapi/editor/ex/PrioritizedDocumentListener.java b/platform/core-impl/src/com/intellij/openapi/editor/ex/PrioritizedDocumentListener.java
index 087340cbacc3..40510a7cd79f 100644
--- a/platform/core-impl/src/com/intellij/openapi/editor/ex/PrioritizedDocumentListener.java
+++ b/platform/core-impl/src/com/intellij/openapi/editor/ex/PrioritizedDocumentListener.java
@@ -41,6 +41,7 @@ public interface PrioritizedDocumentListener extends DocumentListener {
     }
 
     private int getPriority(Object o) {
+      assert o != null;
       if (o instanceof PrioritizedDocumentListener) return ((PrioritizedDocumentListener)o).getPriority();
       return Integer.MAX_VALUE;
     }
diff --git a/platform/core-impl/src/com/intellij/openapi/editor/impl/DocumentImpl.java b/platform/core-impl/src/com/intellij/openapi/editor/impl/DocumentImpl.java
index 437d7233a42c..f699133c0487 100644
--- a/platform/core-impl/src/com/intellij/openapi/editor/impl/DocumentImpl.java
+++ b/platform/core-impl/src/com/intellij/openapi/editor/impl/DocumentImpl.java
@@ -679,7 +679,8 @@ public class DocumentImpl extends UserDataHolderBase implements DocumentEx {
   private DocumentListener[] getCachedListeners() {
     DocumentListener[] cachedListeners = myCachedDocumentListeners;
     if (cachedListeners == null) {
-      DocumentListener[] listeners = myDocumentListeners.toArray(new DocumentListener[myDocumentListeners.size()]);
+      List<DocumentListener> copy = new ArrayList<DocumentListener>(myDocumentListeners);
+      DocumentListener[] listeners = copy.toArray(new DocumentListener[copy.size()]);
       Arrays.sort(listeners, PrioritizedDocumentListener.COMPARATOR);
       myCachedDocumentListeners = cachedListeners = listeners;
     }