diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 6cc5fccac46..9e282f8f673 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -526,6 +526,9 @@ Bug fixes
 * LUCENE-2634: isCurrent on an NRT reader was failing to return false
   if the writer had just committed (Nikolay Zamosenchuk via Mike McCandless)
 
+* LUCENE-2650: Added extra safety to MMapIndexInput clones to prevent accessing
+  an unmapped buffer if the input is closed (Mike McCandless, Uwe Schindler, Robert Muir) 
+
 New features
 
 * LUCENE-2128: Parallelized fetching document frequencies during weight
diff --git a/lucene/src/java/org/apache/lucene/store/MMapDirectory.java b/lucene/src/java/org/apache/lucene/store/MMapDirectory.java
index 58be3678ccb..596ffd539b0 100644
--- a/lucene/src/java/org/apache/lucene/store/MMapDirectory.java
+++ b/lucene/src/java/org/apache/lucene/store/MMapDirectory.java
@@ -259,6 +259,8 @@ public class MMapDirectory extends FSDirectory {
 
     @Override
     public Object clone() {
+      if (buffer == null)
+        throw new AlreadyClosedException("MMapIndexInput already closed");
       MMapIndexInput clone = (MMapIndexInput)super.clone();
       clone.isClone = true;
       clone.buffer = buffer.duplicate();
@@ -267,9 +269,9 @@ public class MMapDirectory extends FSDirectory {
 
     @Override
     public void close() throws IOException {
-      if (isClone || buffer == null) return;
       // unmap the buffer (if enabled) and at least unset it for GC
       try {
+        if (isClone || buffer == null) return;
         cleanMapping(buffer);
       } finally {
         buffer = null;
@@ -382,6 +384,8 @@ public class MMapDirectory extends FSDirectory {
   
     @Override
     public Object clone() {
+      if (buffers == null)
+        throw new AlreadyClosedException("MultiMMapIndexInput already closed");
       MultiMMapIndexInput clone = (MultiMMapIndexInput)super.clone();
       clone.isClone = true;
       clone.buffers = new ByteBuffer[buffers.length];
@@ -403,8 +407,8 @@ public class MMapDirectory extends FSDirectory {
   
     @Override
     public void close() throws IOException {
-      if (isClone || buffers == null) return;
       try {
+        if (isClone || buffers == null) return;
         for (int bufNr = 0; bufNr < buffers.length; bufNr++) {
           // unmap the buffer (if enabled) and at least unset it for GC
           try {