diff --git a/doomsday/libdeng2/include/de/data/stringpool.h b/doomsday/libdeng2/include/de/data/stringpool.h
index b8b03a7139..0a04a435fb 100644
--- a/doomsday/libdeng2/include/de/data/stringpool.h
+++ b/doomsday/libdeng2/include/de/data/stringpool.h
@@ -223,7 +223,7 @@ class DENG2_PUBLIC StringPool : public ISerializable
      * @return  @c 0 iff iteration completed wholly. Otherwise the non-zero value
      *          returned by @a callback.
      */
-    int iterate(int (*callback)(Id, void *), void *data) const;
+    int iterate(int (*callback)(Id, void *), void *data = 0) const;
 
     // Implements ISerializable.
     void operator >> (Writer &to) const;