diff --git a/lib/ace/edit_session.js b/lib/ace/edit_session.js
index a81bf5ed..5c9c2baa 100644
--- a/lib/ace/edit_session.js
+++ b/lib/ace/edit_session.js
@@ -1021,7 +1021,7 @@ var EditSession = function(text, mode) {
             } else {
                 lastRow = firstRow;
             }
-            len = e.data.lines.length;
+            len = e.data.lines ? e.data.lines.length : lastRow - firstRow;
         } else {
             len = lastRow - firstRow;
         }