Index: core/src/main/scala/kafka/message/ByteBufferMessageSet.scala
===================================================================
--- core/src/main/scala/kafka/message/ByteBufferMessageSet.scala	(revision 1160872)
+++ core/src/main/scala/kafka/message/ByteBufferMessageSet.scala	(working copy)
@@ -68,7 +68,8 @@
         shallowValidByteCount = messageAndOffset.offset
       }
     }
-    shallowValidByteCount - initialOffset
+    if(shallowValidByteCount < initialOffset) 0
+    else (shallowValidByteCount - initialOffset)
   }
   
   def deepValidBytes: Long = {