diff --git a/vlib/compiler/cc.v b/vlib/compiler/cc.v
index 0fa19bc0aa..4225ab8236 100644
--- a/vlib/compiler/cc.v
+++ b/vlib/compiler/cc.v
@@ -135,7 +135,7 @@ fn (v mut V) cc() {
 	}
 
 	if v.pref.ccompiler != 'msvc' && v.os != .freebsd {
-		//a << '-Werror=implicit-function-declaration'
+		a << '-Werror=implicit-function-declaration'
 	}
 
 	for f in v.generate_hotcode_reloading_compiler_flags() {