diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index 573a53edb8..76f3731020 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -589,10 +589,18 @@
 #define SIZEOF_LONG 4
 
 /* The size of `size_t', as computed by sizeof. */
+#ifndef _WIN64
 #define SIZEOF_SIZE_T 4
+#else
+#define SIZEOF_SIZE_T 8
+#endif
 
 /* The size of `void *', as computed by sizeof. */
+#ifndef _WIN64
 #define SIZEOF_VOID_P 4
+#else
+#define SIZEOF_VOID_P 8
+#endif
 
 /* Define to 1 if you have the ANSI C header files. */
 #define STDC_HEADERS 1