diff --git a/src/lib.rs b/src/lib.rs
index 3fbe0fa..45aff14 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -357,7 +357,7 @@
 //! See [LICENSE](LICENSE) for details.
 //!
 
-#![warn(missing_docs)]
+#![deny(missing_docs)]
 
 #[cfg(feature = "regex_support")]
 extern crate regex;