diff --git a/js/src/ctypes/CTypes.cpp b/js/src/ctypes/CTypes.cpp
index 1a8c21e402f..36cd2df0209 100644
--- a/js/src/ctypes/CTypes.cpp
+++ b/js/src/ctypes/CTypes.cpp
@@ -3944,9 +3944,8 @@ StructType::DefineInternal(JSContext* cx, JSObject* typeObj, JSObject* fieldsObj
     return JS_FALSE;
 
   // Create a hash of FieldInfo objects to stash on the type object.
-  FieldInfoHash* fields(new FieldInfoHash);
+  AutoPtr<FieldInfoHash> fields(new FieldInfoHash);
   if (!fields || !fields->init(len)) {
-    delete fields;
     JS_ReportOutOfMemory(cx);
     return JS_FALSE;
   }
@@ -3954,8 +3953,9 @@ StructType::DefineInternal(JSContext* cx, JSObject* typeObj, JSObject* fieldsObj
   // Stash the FieldInfo hash in a reserved slot now, for GC safety of its
   // constituents.
   if (!JS_SetReservedSlot(cx, typeObj, SLOT_FIELDINFO,
-         PRIVATE_TO_JSVAL(fields)))
+         PRIVATE_TO_JSVAL(fields.get())))
     return JS_FALSE;
+  fields.forget();
 
   // Process the field types.
   size_t structSize, structAlign;