diff --git a/src/api/sockets.c b/src/api/sockets.c
index b7632489..f6ab59f6 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -44,6 +44,8 @@
  *
  */
 
+#include <errno.h>
+
 #include "lwip/opt.h"
 
 #if LWIP_SOCKET /* don't build if not configured for use in lwipopts.h */