diff --git a/book/src/types/role_of_interner.md b/book/src/types/role_of_interner.md
index f52d5d828b7..a033857407f 100644
--- a/book/src/types/role_of_interner.md
+++ b/book/src/types/role_of_interner.md
@@ -72,7 +72,7 @@ and
 
 ```rust,ignore
 impl<I: Interner> TyData<I> {
-  fn intern(&self, I: &I) -> Ty<I> {
+  fn intern(&self, i: &I) -> Ty<I> {
     Ty(i.intern_ty(self))
   }
 }