diff --git a/include/uv/errno.h b/include/uv/errno.h
index 165fd11c..8d4d7686 100644
--- a/include/uv/errno.h
+++ b/include/uv/errno.h
@@ -317,7 +317,7 @@
 #if defined(EPROTO) && !defined(_WIN32)
 # define UV__EPROTO UV__ERR(EPROTO)
 #else
-# define UV__EPROTO UV__ERR(4046)
+# define UV__EPROTO UV__ERR(-4046)
 #endif
 
 #if defined(EPROTONOSUPPORT) && !defined(_WIN32)