diff --git a/lib/ace/layer/gutter.js b/lib/ace/layer/gutter.js
index 503cc93a..2a8ea96e 100644
--- a/lib/ace/layer/gutter.js
+++ b/lib/ace/layer/gutter.js
@@ -129,7 +129,8 @@ var Gutter = function(parentEl) {
 
             if (foldWidgets) {
                 var c = foldWidgets[i];
-                if (!c)
+                // check if cached value is invalidated and we need to recompute
+                if (c == null)
                     c = foldWidgets[i] = this.session.getFoldWidget(i);
                 if (c)
                     html.push(
diff --git a/lib/ace/mode/folding/fold_mode.js b/lib/ace/mode/folding/fold_mode.js
index 1f941c00..d231a35f 100644
--- a/lib/ace/mode/folding/fold_mode.js
+++ b/lib/ace/mode/folding/fold_mode.js
@@ -48,6 +48,7 @@ var FoldMode = exports.FoldMode = function() {};
     this.foldingStartMarker = null;
     this.foldingStopMarker = null;
 
+    // must return "" if there's no fold, to enable caching
     this.getFoldWidget = function(session, row) {
         if (this.foldingStartMarker) {
             if (this.foldingStopMarker)
diff --git a/lib/ace/mode/folding/xml.js b/lib/ace/mode/folding/xml.js
index 06aa3167..0e5802a5 100644
--- a/lib/ace/mode/folding/xml.js
+++ b/lib/ace/mode/folding/xml.js
@@ -66,13 +66,13 @@ oop.inherits(FoldMode, BaseFoldMode);
         var fold = tags[0];
         
         if (!fold || this.voidElements[fold])
-            return;
+            return "";
             
         if (fold.charAt(0) == "/")
             return "end";
             
         if (tags.indexOf("/" + fold) !== -1)
-            return;
+            return "";
             
         return "start";
     };