diff --git a/vlib/builtin/builtin.v b/vlib/builtin/builtin.v
index ba6c8c8c07..7f83d0ef76 100644
--- a/vlib/builtin/builtin.v
+++ b/vlib/builtin/builtin.v
@@ -5,7 +5,7 @@
 module builtin
 
 // isnil returns true if an object is nil (only for C objects).
-@[inline]
+@[inline; markused]
 pub fn isnil(v voidptr) bool {
 	return v == 0
 }