diff --git a/clang/lib/AST/NestedNameSpecifier.cpp b/clang/lib/AST/NestedNameSpecifier.cpp
index a514d57..df23972 100644
--- a/clang/lib/AST/NestedNameSpecifier.cpp
+++ b/clang/lib/AST/NestedNameSpecifier.cpp
@@ -547,6 +547,7 @@
   }
 
   // Deep copy.
+  BufferSize = 0;
   Append(Other.Buffer, Other.Buffer + Other.BufferSize, Buffer, BufferSize,
          BufferCapacity);
   return *this;