diff --git a/src/libstrongswan/utils/windows.h b/src/libstrongswan/utils/windows.h
index 053354f25..a06a89ebf 100644
--- a/src/libstrongswan/utils/windows.h
+++ b/src/libstrongswan/utils/windows.h
@@ -361,6 +361,11 @@ ssize_t windows_send(int sockfd, const void *buf, size_t len, int flags);
 ssize_t windows_sendto(int sockfd, const void *buf, size_t len, int flags,
 					   const struct sockaddr *dest_addr, socklen_t addrlen);
 
+/**
+ * Declaration missing on older WinGW
+ */
+_CRTIMP errno_t strerror_s(char *buf, size_t size, int errnum);
+
 /**
  * strerror_s, but supporting POSIX compatiblity errno >= 100
  */