diff --git a/lib/ace/edit_session/folding.js b/lib/ace/edit_session/folding.js
index b36857c6..1735e6f9 100644
--- a/lib/ace/edit_session/folding.js
+++ b/lib/ace/edit_session/folding.js
@@ -272,7 +272,8 @@ function Folding() {
         var endColumn = fold.end.column;
 
         // --- Some checking ---
-        if (startRow == endRow && endColumn - startColumn < 2)
+        if (!(startRow < endRow || 
+            startRow == endRow && startColumn < endColumn - 2))
             throw "The range has to be at least 2 characters width";
 
         var startFold = this.getFoldAt(startRow, startColumn, 1);
@@ -627,19 +628,25 @@ function Folding() {
             depth = 100000; // JSON.stringify doesn't hanle Infinity
         var foldWidgets = this.foldWidgets;
         endRow = endRow || this.getLength();
-        for (var row = startRow || 0; row < endRow; row++) {
+        startRow = startRow || 0;
+        for (var row = startRow; row < endRow; row++) {
             if (foldWidgets[row] == null)
                 foldWidgets[row] = this.getFoldWidget(row);
             if (foldWidgets[row] != "start")
                 continue;
 
             var range = this.getFoldWidgetRange(row);
+            var rangeEndRow = range.end.row;
             // sometimes range can be incompatible with existing fold
             // TODO change addFold to return null istead of throwing
-            if (range && range.end.row <= endRow) try {
+            if (range && range.isMultiLine()
+                && rangeEndRow <= endRow
+                && range.start.row >= startRow
+            ) try {
                 var fold = this.addFold("...", range);
                 fold.collapseChildren = depth;
-                row = range.end.row;
+                // addFold can change the range
+                row = rangeEndRow;
             } catch(e) {}
         }
     };