diff --git a/components/style/build_gecko.rs b/components/style/build_gecko.rs
index 1e93660936a..1f034cad934 100644
--- a/components/style/build_gecko.rs
+++ b/components/style/build_gecko.rs
@@ -279,7 +279,7 @@ impl<'a> BuilderWithConfig<'a> {
     fn get_builder(self) -> Builder {
         for key in self.config.keys() {
             if !self.used_keys.contains(key.as_str()) {
-                panic!(format!("Unknown key: {}", key));
+                panic!("Unknown key: {}", key);
             }
         }
         self.builder