diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index b92312d5276..15f00017555 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -108,7 +108,7 @@ impl MacroRules {
 
         // Note that TokenId is started from zero,
         // We have to add 1 to prevent duplication.
-        let shift = max_id(tt).unwrap_or(0) + 1;
+        let shift = max_id(tt).map_or(0, |it| it + 1);
         Ok(MacroRules { rules, shift })
     }