diff --git a/clang/include/clang/AST/DeclContextInternals.h b/clang/include/clang/AST/DeclContextInternals.h
index 42cc677f82135..e169c48592192 100644
--- a/clang/include/clang/AST/DeclContextInternals.h
+++ b/clang/include/clang/AST/DeclContextInternals.h
@@ -42,11 +42,12 @@ class StoredDeclsList {
   /// external declarations.
   DeclsAndHasExternalTy Data;
 
-  template<typename Fn>
-  void erase_if(Fn ShouldErase) {
+  template <typename Fn> DeclListNode::Decls *erase_if(Fn ShouldErase) {
     Decls List = Data.getPointer();
+
     if (!List)
-      return;
+      return nullptr;
+
     ASTContext &C = getASTContext();
     DeclListNode::Decls NewHead = nullptr;
     DeclListNode::Decls *NewLast = nullptr;
@@ -79,6 +80,17 @@ class StoredDeclsList {
     Data.setPointer(NewHead);
 
     assert(llvm::none_of(getLookupResult(), ShouldErase) && "Still exists!");
+
+    if (!Data.getPointer())
+      // All declarations are erased.
+      return nullptr;
+    else if (NewHead.is<NamedDecl *>())
+      // The list only contains a declaration, the header itself.
+      return (DeclListNode::Decls *)&Data;
+    else {
+      assert(NewLast && NewLast->is<NamedDecl *>() && "Not the tail?");
+      return NewLast;
+    }
   }
 
   void erase(NamedDecl *ND) {
@@ -161,7 +173,7 @@ class StoredDeclsList {
   void replaceExternalDecls(ArrayRef<NamedDecl*> Decls) {
     // Remove all declarations that are either external or are replaced with
     // external declarations with higher visibilities.
-    erase_if([Decls](NamedDecl *ND) {
+    DeclListNode::Decls *Tail = erase_if([Decls](NamedDecl *ND) {
       if (ND->isFromASTFile())
         return true;
       // FIXME: Can we get rid of this loop completely?
@@ -189,24 +201,15 @@ class StoredDeclsList {
       DeclsAsList = Node;
     }
 
-    DeclListNode::Decls Head = Data.getPointer();
-    if (Head.isNull()) {
+    if (!Data.getPointer()) {
       Data.setPointer(DeclsAsList);
       return;
     }
 
-    // Find the end of the existing list.
-    // FIXME: It would be possible to preserve information from erase_if to
-    // avoid this rescan looking for the end of the list.
-    DeclListNode::Decls *Tail = &Head;
-    while (DeclListNode *Node = Tail->dyn_cast<DeclListNode *>())
-      Tail = &Node->Rest;
-
     // Append the Decls.
     DeclListNode *Node = C.AllocateDeclListNode(Tail->get<NamedDecl *>());
     Node->Rest = DeclsAsList;
     *Tail = Node;
-    Data.setPointer(Head);
   }
 
   /// Return the list of all the decls.