diff --git a/clang/lib/Checker/RegionStore.cpp b/clang/lib/Checker/RegionStore.cpp
index 1603cc8..d9ad02a 100644
--- a/clang/lib/Checker/RegionStore.cpp
+++ b/clang/lib/Checker/RegionStore.cpp
@@ -280,8 +280,12 @@
 
   Store Bind(Store store, Loc LV, SVal V);
 
+  // BindDefault is only used to initialize a region with a default value.
   Store BindDefault(Store store, const MemRegion *R, SVal V) {
-    return Add(GetRegionBindings(store), R, BindingKey::Default, V).getRoot();
+    RegionBindings B = GetRegionBindings(store);
+    assert(!Lookup(B, R, BindingKey::Default));
+    assert(!Lookup(B, R, BindingKey::Direct));
+    return Add(B, R, BindingKey::Default, V).getRoot();
   }
 
   Store BindCompoundLiteral(Store store, const CompoundLiteralExpr* CL,