Index: libmapi/IStream.c
===================================================================
--- libmapi/IStream.c	(revision 1351)
+++ libmapi/IStream.c	(working copy)
@@ -674,7 +674,7 @@
 	OPENCHANGE_RETVAL_IF(!session[1], MAPI_E_INVALID_PARAMETER, NULL);
 	OPENCHANGE_RETVAL_IF(session[0] != session[1], MAPI_E_INVALID_PARAMETER, NULL);
 
-	OPENCHANGE_RETVAL_IF(!ByteCount, MAPI_E_INVALID_PARAMETER, NULL);
+	OPENCHANGE_RETVAL_IF(ByteCount > 0, MAPI_E_INVALID_PARAMETER, NULL);
 	OPENCHANGE_RETVAL_IF(!ReadByteCount, MAPI_E_INVALID_PARAMETER, NULL);
 	OPENCHANGE_RETVAL_IF(!WrittenByteCount, MAPI_E_INVALID_PARAMETER, NULL);