diff --git a/vlib/builtin/cfns.v b/vlib/builtin/cfns.v
index 49a887f058..063f16d43f 100644
--- a/vlib/builtin/cfns.v
+++ b/vlib/builtin/cfns.v
@@ -147,4 +147,5 @@ fn C.CloseHandle()
 fn C.WaitForSingleObject()
 fn C.GetExitCodeProcess()
 fn C.RegOpenKeyEx() voidptr
-fn C.GetTickCount() i64
\ No newline at end of file
+fn C.GetTickCount() i64
+fn C.Sleep()
\ No newline at end of file