diff --git a/lib/ajax/section_classes.js b/lib/ajax/section_classes.js
index b228110..3481f59 100755
--- a/lib/ajax/section_classes.js
+++ b/lib/ajax/section_classes.js
@@ -729,7 +729,11 @@ resource_class.prototype.indent_left = function() {
         }
         return false;
     }
-    var oldindent = indentdiv.classList.toString().match(/mod-indent-(\d{1,})/);
+    if (document.documentElement.classList)
+        var oldindent = indentdiv.classList.toString().match(/mod-indent-(\d{1,})/);
+    else {
+        var oldindent = (new RegExp('mod-indent-(\\d{1,})')).exec(indentdiv.className);
+    }
     if (oldindent && oldindent[1] > 0) {
         oldindent = oldindent[1];
     } else {
@@ -760,7 +764,11 @@ resource_class.prototype.indent_right = function() {
         }
         return false;
     }
-    var oldindent = indentdiv.classList.toString().match(/mod-indent-(\d{1,})/);
+    if (document.documentElement.classList)
+        var oldindent = indentdiv.classList.toString().match(/mod-indent-(\d{1,})/);
+    else {
+        var oldindent = (new RegExp('mod-indent-(\\d{1,})')).exec(indentdiv.className);
+    }
     if (oldindent && oldindent[1] >= 0) {
         oldindent = oldindent[1];
         var newindent = parseFloat(oldindent) + 1;