diff --git a/macros/src/codegen/util.rs b/macros/src/codegen/util.rs
index 887ee3bdfc..d78da61d13 100644
--- a/macros/src/codegen/util.rs
+++ b/macros/src/codegen/util.rs
@@ -53,7 +53,7 @@ pub fn impl_mutex(
             type T = #ty;
 
             #[inline(always)]
-            fn lock<R>(&mut self, f: impl FnOnce(&mut #ty) -> R) -> R {
+            fn lock<RTIC_INTERNAL_R>(&mut self, f: impl FnOnce(&mut #ty) -> RTIC_INTERNAL_R) -> RTIC_INTERNAL_R {
                 /// Priority ceiling
                 const CEILING: u8 = #ceiling;