Index: lucene/core/src/java/org/apache/lucene/index/IndexReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/IndexReader.java	(revision 1548710)
+++ lucene/core/src/java/org/apache/lucene/index/IndexReader.java	(working copy)
@@ -168,8 +168,9 @@
    * @see #tryIncRef
    */
   public final void incRef() {
-    ensureOpen();
-    refCount.incrementAndGet();
+    if (!tryIncRef()) {
+       ensureOpen();
+    }
   }
   
   /**
Index: lucene/core/src/java/org/apache/lucene/index/SegmentCoreReaders.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/SegmentCoreReaders.java	(revision 1548710)
+++ lucene/core/src/java/org/apache/lucene/index/SegmentCoreReaders.java	(working copy)
@@ -32,6 +32,7 @@
 import org.apache.lucene.codecs.StoredFieldsReader;
 import org.apache.lucene.codecs.TermVectorsReader;
 import org.apache.lucene.index.SegmentReader.CoreClosedListener;
+import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.CompoundFileDirectory;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.IOContext;
@@ -139,7 +140,13 @@
   }
   
   void incRef() {
-    ref.incrementAndGet();
+    int count;
+    while ((count = ref.get()) > 0) {
+      if (ref.compareAndSet(count, count+1)) {
+        return;
+      }
+    }
+    throw new AlreadyClosedException("SegmentCoreReaders is already closed");
   }
 
   NumericDocValues getNormValues(FieldInfo fi) throws IOException {