diff --git a/compiler/rustc_index/src/vec.rs b/compiler/rustc_index/src/vec.rs
index 1cb8bc861af98..796c2b7c34b8b 100644
--- a/compiler/rustc_index/src/vec.rs
+++ b/compiler/rustc_index/src/vec.rs
@@ -39,7 +39,7 @@ use crate::{Idx, IndexSlice};
 #[repr(transparent)]
 pub struct IndexVec<I: Idx, T> {
     pub raw: Vec<T>,
-    _marker: PhantomData<fn(&I)>,
+    _marker: PhantomData<I>,
 }
 
 impl<I: Idx, T> IndexVec<I, T> {