diff --git a/cranelift/isle/isle/src/codegen.rs b/cranelift/isle/isle/src/codegen.rs
index 844d5c8b49..6968302286 100644
--- a/cranelift/isle/isle/src/codegen.rs
+++ b/cranelift/isle/isle/src/codegen.rs
@@ -71,7 +71,7 @@ impl<'a> Codegen<'a> {
             "#![allow(unused_imports, unused_variables, non_snake_case)]"
         )
         .unwrap();
-        writeln!(code, "#[allow(irrefutable_let_patterns)]").unwrap();
+        writeln!(code, "#![allow(irrefutable_let_patterns)]").unwrap();
 
         writeln!(code, "\nuse super::*;  // Pulls in all external types.").unwrap();
     }