diff --git a/naga/src/back/msl/writer.rs b/naga/src/back/msl/writer.rs
index 1bae7f2f62..206e546687 100644
--- a/naga/src/back/msl/writer.rs
+++ b/naga/src/back/msl/writer.rs
@@ -599,11 +599,23 @@ impl crate::Type {
     }
 }
 
+#[derive(Clone, Copy)]
 enum FunctionOrigin {
     Handle(Handle<crate::Function>),
     EntryPoint(proc::EntryPointIndex),
 }
 
+trait NameKeyExt {
+    fn local(origin: FunctionOrigin, local_handle: Handle<crate::LocalVariable>) -> NameKey {
+        match origin {
+            FunctionOrigin::Handle(handle) => NameKey::FunctionLocal(handle, local_handle),
+            FunctionOrigin::EntryPoint(idx) => NameKey::EntryPointLocal(idx, local_handle),
+        }
+    }
+}
+
+impl NameKeyExt for NameKey {}
+
 /// A level of detail argument.
 ///
 /// When [`BoundsCheckPolicy::Restrict`] applies to an [`ImageLoad`] access, we
@@ -1750,14 +1762,7 @@ impl<W: Write> Writer<W> {
                 write!(self.out, "{name}")?;
             }
             crate::Expression::LocalVariable(handle) => {
-                let name_key = match context.origin {
-                    FunctionOrigin::Handle(fun_handle) => {
-                        NameKey::FunctionLocal(fun_handle, handle)
-                    }
-                    FunctionOrigin::EntryPoint(ep_index) => {
-                        NameKey::EntryPointLocal(ep_index, handle)
-                    }
-                };
+                let name_key = NameKey::local(context.origin, handle);
                 let name = &self.names[&name_key];
                 write!(self.out, "{name}")?;
             }