diff --git a/include/SDL_config.h.cmake b/include/SDL_config.h.cmake
index 8423be702..12c14fa24 100644
--- a/include/SDL_config.h.cmake
+++ b/include/SDL_config.h.cmake
@@ -37,7 +37,13 @@
 #cmakedefine volatile @HAVE_VOLATILE@
 
 /* C datatypes */
-#cmakedefine SIZEOF_VOIDP @SIZEOF_VOIDP@
+/* Define SIZEOF_VOIDP for 64/32 architectures */
+#ifdef __LP64__
+#define SIZEOF_VOIDP 8
+#else
+#define SIZEOF_VOIDP 4
+#endif
+
 #cmakedefine HAVE_GCC_ATOMICS @HAVE_GCC_ATOMICS@
 #cmakedefine HAVE_GCC_SYNC_LOCK_TEST_AND_SET @HAVE_GCC_SYNC_LOCK_TEST_AND_SET@
 #cmakedefine HAVE_PTHREAD_SPINLOCK @HAVE_PTHREAD_SPINLOCK@
diff --git a/include/SDL_config.h.in b/include/SDL_config.h.in
index 7c5d9bf97..d751d8ed9 100644
--- a/include/SDL_config.h.in
+++ b/include/SDL_config.h.in
@@ -43,6 +43,11 @@
 
 /* C datatypes */
 #undef SIZEOF_VOIDP
+#ifdef __LP64__
+#define SIZEOF_VOID_P 8
+#else
+#define SIZEOF_VOID_P 4
+#endif
 #undef HAVE_GCC_ATOMICS
 #undef HAVE_GCC_SYNC_LOCK_TEST_AND_SET
 #undef HAVE_PTHREAD_SPINLOCK