diff --git a/serde/src/lib.rs b/serde/src/lib.rs
index 5473f822..10461f46 100644
--- a/serde/src/lib.rs
+++ b/serde/src/lib.rs
@@ -149,6 +149,8 @@
         must_use_candidate,
     )
 )]
+// Restrictions
+#![cfg_attr(feature = "cargo-clippy", deny(question_mark_used))]
 // Rustc lints.
 #![deny(missing_docs, unused_imports)]