diff --git a/lib/config-win32.h b/lib/config-win32.h
index 4cac859cd..3d7892fec 100644
--- a/lib/config-win32.h
+++ b/lib/config-win32.h
@@ -406,6 +406,9 @@
 #  define SIZEOF_SIZE_T 4
 #endif
 
+/* Define to the size of `curl_off_t', as computed by sizeof. */
+#define SIZEOF_CURL_OFF_T 8
+
 /* ---------------------------------------------------------------- */
 /*               BSD-style lwIP TCP/IP stack SPECIFIC               */
 /* ---------------------------------------------------------------- */