diff --git a/ext/gmp/php_gmp_int.h b/ext/gmp/php_gmp_int.h
index d4ef5f0157332..c37fdb136d023 100644
--- a/ext/gmp/php_gmp_int.h
+++ b/ext/gmp/php_gmp_int.h
@@ -28,7 +28,7 @@ static inline gmp_object *php_gmp_object_from_zend_object(zend_object *zobj) {
 PHP_GMP_API zend_class_entry *php_gmp_class_entry(void);
 
 /* GMP and MPIR use different datatypes on different platforms */
-#ifdef PHP_WIN32
+#ifdef _WIN64
 typedef zend_long gmp_long;
 typedef zend_ulong gmp_ulong;
 #else