diff --git a/crypto/compat/posix_win.c b/crypto/compat/posix_win.c
index f8121d8..d6e2dcb 100644
--- a/crypto/compat/posix_win.c
+++ b/crypto/compat/posix_win.c
@@ -209,6 +209,7 @@ posix_setsockopt(int sockfd, int level, int optname,
 }
 
 #ifdef _MSC_VER
+struct timezone;
 int gettimeofday(struct timeval * tp, struct timezone * tzp)
 {
 	/*