diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index b0a0131536b..9976b0e9862 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -672,7 +672,7 @@ impl<'hir> Map<'hir> {
         }
     }
 
-    pub fn for_each_module(self, f: impl Fn(LocalDefId)) {
+    pub fn for_each_module(self, mut f: impl FnMut(LocalDefId)) {
         let crate_items = self.tcx.hir_crate_items(());
         for module in crate_items.submodules.iter() {
             f(*module)