Index: lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(revision 1556823)
+++ lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -17,24 +17,6 @@
  * limitations under the License.
  */
 
-import java.io.Closeable;
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.Date;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.Iterator;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Locale;
-import java.util.Map;
-import java.util.Map.Entry;
-import java.util.Queue;
-import java.util.Set;
-import java.util.concurrent.atomic.AtomicInteger;
-
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.index.FieldInfo.DocValuesType;
@@ -58,6 +40,24 @@
 import org.apache.lucene.util.InfoStream;
 import org.apache.lucene.util.ThreadInterruptedException;
 
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Queue;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
+
 /**
   An <code>IndexWriter</code> creates and maintains an index.
 
@@ -930,10 +930,20 @@
           closeInternal(waitForMerges, true);
         }
       }
-      assert eventQueue.isEmpty();
+      assert assertEventQueueAfterClose();
     }
   }
 
+  private boolean assertEventQueueAfterClose() {
+    if (eventQueue.isEmpty()) {
+      return true;
+    }
+    for (Event e : eventQueue) {
+      assert e instanceof DocumentsWriter.MergePendingEvent : e;
+    }
+    return true;
+  }
+
   // Returns true if this thread should attempt to close, or
   // false if IndexWriter is now closed; else, waits until
   // another thread finishes closing
@@ -2022,7 +2032,7 @@
         rollbackInternal();
       }
     }
-    assert eventQueue.isEmpty() : eventQueue;
+    assert assertEventQueueAfterClose();
   }
 
   private void rollbackInternal() throws IOException {