diff --git a/include/wx/hashmap.h b/include/wx/hashmap.h
index 316abdec50..9b635e8a07 100644
--- a/include/wx/hashmap.h
+++ b/include/wx/hashmap.h
@@ -16,8 +16,6 @@
 #pragma interface "hashmap.h"
 #endif
 
-#include <stddef.h>         // for ptrdiff_t
-
 #include "wx/string.h"
 
 // private