diff --git a/lib/curl_strerror.c b/lib/curl_strerror.c
index 1152aca4c3aa117592892b6a464e77d5abee9491..0d4ecbef8356ad89ed1786002530c89a6693cc41 100644
--- a/lib/curl_strerror.c
+++ b/lib/curl_strerror.c
@@ -488,6 +488,8 @@ get_winsock_error (int err, char *buf, size_t len)
 }
 #endif   /* WIN32 && !__CYGWIN__ */
 
+extern int sys_nerr;
+
 /*
  * Our thread-safe and smart strerror() replacement.
  */