diff --git a/src/main/com/mongodb/CommandResult.java b/src/main/com/mongodb/CommandResult.java
index 5ba432452af..fed01a7b005 100644
--- a/src/main/com/mongodb/CommandResult.java
+++ b/src/main/com/mongodb/CommandResult.java
@@ -70,7 +70,9 @@ public MongoException getException() {
         if ( !ok() ) {   // check for command failure
             return new CommandFailureException( this );
         } else if ( hasErr() ) { // check for errors reported by getlasterror command
-            if (getCode() == 11000 || getCode() == 11001 || getCode() == 12582) {
+            String err = getErr();
+            if (getCode() == 11000 || getCode() == 11001 || getCode() == 12582 ||
+                    err.startsWith("E11000") || err.startsWith("E11001")) {
                 return new MongoException.DuplicateKey(this);
             }
             else {
@@ -92,13 +94,17 @@ int getCode() {
         return code;
     }
 
+    String getErr() {
+        return (String) get("err");
+    }
+
     /**
      * check the "err" field
      * @return if it has it, and isn't null
      */
     boolean hasErr(){
-        Object o = get( "err" );
-        return (o != null && ( (String) o ).length() > 0 );
+        String o = getErr();
+        return (o != null && !o.isEmpty());
     }
 
     /**
diff --git a/src/test/com/mongodb/CommandResultTest.java b/src/test/com/mongodb/CommandResultTest.java
index 6bee150ef62..792d6cc0f6c 100644
--- a/src/test/com/mongodb/CommandResultTest.java
+++ b/src/test/com/mongodb/CommandResultTest.java
@@ -57,4 +57,21 @@ public void testCommandFailure() throws UnknownHostException {
             assertEquals(5000, e.getCode());
         }
     }
+
+    /**
+     * mongoS return an "err" but don't return a "code" for duplicate key errors
+     */
+    @Test
+    public void testCommandDuplicateKeyWithoutCode() throws UnknownHostException {
+        CommandResult commandResult = new CommandResult(new ServerAddress("localhost"));
+        final DBObject result = new BasicDBObject("ok", 1.0).append("err", "E11000 duplicate key error index");
+        commandResult.putAll(result);
+        assertEquals(MongoException.DuplicateKey.class, commandResult.getException().getClass());
+        try {
+            commandResult.throwOnError();
+            fail("Should throw");
+        } catch (MongoException.DuplicateKey e) {
+            assertEquals(commandResult, e.getCommandResult());
+        }
+    }
 }