diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -1344,6 +1344,10 @@
     PrevDecl = D;
   }
 
+  if (PrevDecl)
+    // Last item in the linked list should have a null next pointer.
+    PrevDecl->NextInContextAndBits.setPointer(nullptr);
+
   return std::make_pair(FirstNewDecl, PrevDecl);
 }