diff --git a/vlib/sync/sync_macos.c.v b/vlib/sync/sync_macos.c.v
index 8fda9dce3f..8c3e320039 100644
--- a/vlib/sync/sync_macos.c.v
+++ b/vlib/sync/sync_macos.c.v
@@ -7,6 +7,7 @@ import time
 
 #flag -lpthread
 #include <semaphore.h>
+#include <sys/errno.h>
 
 [trusted]
 fn C.pthread_mutex_init(voidptr, voidptr) int