diff --git a/src/api/sockets.c b/src/api/sockets.c
index a0c24829..a6d682cb 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -38,7 +38,8 @@
  */
 
 #include "lwip/opt.h"
-#include "ZeroTierConstants.h"
+
+extern int zts_errno;
 
 #if LWIP_SOCKET /* don't build if not configured for use in lwipopts.h */