diff -u b/core/misc/collapse.js b/core/misc/collapse.js
--- b/core/misc/collapse.js
+++ b/core/misc/collapse.js
@@ -14,8 +14,7 @@
   };
   this.settings = $.extend(
     defaults,
-    Drupal.settings.collapsibleFieldset,
-    settings || {}
+    settings.collapsibleFieldset || {}
   );
   // Expand fieldset if there are errors inside, or if it contains an
   // element that is targeted by the uri fragment identifier.
@@ -115,7 +114,7 @@
       // Initialize array holding CollapsibleFieldset objects.
       Drupal.CollapsibleFieldset.fieldsets = Drupal.CollapsibleFieldset.fieldsets || [];
       $collapsibleFieldsets.each(function() {
-        Drupal.CollapsibleFieldset.fieldsets.push(new Drupal.CollapsibleFieldset(this), settings);
+        Drupal.CollapsibleFieldset.fieldsets.push(new Drupal.CollapsibleFieldset(this, settings));
       });
     }
   }