diff --git a/components/selectors/builder.rs b/components/selectors/builder.rs
index 33c0ec1b694..b17ed9bfc63 100644
--- a/components/selectors/builder.rs
+++ b/components/selectors/builder.rs
@@ -72,7 +72,7 @@ impl<Impl: SelectorImpl> SelectorBuilder<Impl> {
     /// Pushes a simple selector onto the current compound selector.
     #[inline(always)]
     pub fn push_simple_selector(&mut self, ss: Component<Impl>) {
-        debug_assert!(!ss.is_combinator());
+        assert!(!ss.is_combinator());
         self.simple_selectors.push(ss);
         self.current_len += 1;
     }