diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 4bf84cb465f77..4e66d21214b29 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -320,17 +320,18 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tc
         local: mir::Local,
         layout: Option<TyLayout<'tcx>>,
     ) -> EvalResult<'tcx, TyLayout<'tcx>> {
-        let cell = &frame.locals[local].layout;
-        if cell.get().is_none() {
-            let layout = ::interpret::operand::from_known_layout(layout, || {
-                let local_ty = frame.mir.local_decls[local].ty;
-                let local_ty = self.monomorphize_with_substs(local_ty, frame.instance.substs);
-                self.layout_of(local_ty)
-            })?;
-            cell.set(Some(layout));
+        match frame.locals[local].layout.get() {
+            None => {
+                let layout = ::interpret::operand::from_known_layout(layout, || {
+                    let local_ty = frame.mir.local_decls[local].ty;
+                    let local_ty = self.monomorphize_with_substs(local_ty, frame.instance.substs);
+                    self.layout_of(local_ty)
+                })?;
+                frame.locals[local].layout.set(Some(layout));
+                Ok(layout)
+            }
+            Some(layout) => Ok(layout),
         }
-
-        Ok(cell.get().unwrap())
     }
 
     pub fn str_to_immediate(&mut self, s: &str) -> EvalResult<'tcx, Immediate<M::PointerTag>> {