diff --git a/ActiveSync/SOGoMailObject+ActiveSync.m b/ActiveSync/SOGoMailObject+ActiveSync.m
index e7a5ce540..1d6bd02ac 100644
--- a/ActiveSync/SOGoMailObject+ActiveSync.m
+++ b/ActiveSync/SOGoMailObject+ActiveSync.m
@@ -772,7 +772,8 @@ struct GlobalObjectId {
             }
         }
 
-      return [theContent substringToIndex: i];
+      if (i >= 0)
+        return [theContent substringToIndex: i];
     }
 
   *wasTruncated = 0;