diff --git a/include/SDL_config.h.in b/include/SDL_config.h.in
index d751d8ed9..04ee11052 100644
--- a/include/SDL_config.h.in
+++ b/include/SDL_config.h.in
@@ -42,11 +42,10 @@
 #undef volatile
 
 /* C datatypes */
-#undef SIZEOF_VOIDP
 #ifdef __LP64__
-#define SIZEOF_VOID_P 8
+#define SIZEOF_VOIDP 8
 #else
-#define SIZEOF_VOID_P 4
+#define SIZEOF_VOIDP 4
 #endif
 #undef HAVE_GCC_ATOMICS
 #undef HAVE_GCC_SYNC_LOCK_TEST_AND_SET