diff --git a/src/common.rs b/src/common.rs
index eda77bf19d3..466758f2f86 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -361,13 +361,11 @@ pub(crate) fn monomorphize<T>(&self, value: &T) -> T
     where
         T: TypeFoldable<'tcx> + Copy,
     {
-        if let Some(substs) = self.instance.substs_for_mir_body() {
-            self.tcx
-                .subst_and_normalize_erasing_regions(substs, ty::ParamEnv::reveal_all(), value)
-        } else {
-            self.tcx
-                .normalize_erasing_regions(ty::ParamEnv::reveal_all(), *value)
-        }
+        self.instance.subst_mir_and_normalize_erasing_regions(
+            self.tcx,
+            ty::ParamEnv::reveal_all(),
+            value
+        )
     }
 
     pub(crate) fn clif_type(&self, ty: Ty<'tcx>) -> Option<Type> {