diff --git a/gmp-h.in b/gmp-h.in
index 7deb67a..240d663 100644
--- a/gmp-h.in
+++ b/gmp-h.in
@@ -46,13 +46,11 @@ along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
 #ifndef __GNU_MP__
 #define __GNU_MP__ 5
 
-#define __need_size_t  /* tell gcc stddef.h we only want size_t */
 #if defined (__cplusplus)
 #include <cstddef>     /* for size_t */
 #else
 #include <stddef.h>    /* for size_t */
 #endif
-#undef __need_size_t
 
 /* Instantiated by configure. */
 #if ! defined (__GMP_WITHIN_CONFIGURE)