diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 0fe424b46e..bb7c8e5fdd 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -286,6 +286,9 @@ fn (mut g Gen) gen_fn_decl(node &ast.FnDecl, skip bool) {
 		g.definitions.write_string(s)
 		g.write(s)
 		g.nr_closures++
+		if g.pref.os == .windows {
+			g.error('closures are not yet implemented on windows', node.pos)
+		}
 	}
 	arg_str := g.out.after(arg_start_pos)
 	if node.no_body || ((g.pref.use_cache && g.pref.build_mode != .build_module) && node.is_builtin