Index: change-namespace/ChangeNamespace.cpp
===================================================================
--- change-namespace/ChangeNamespace.cpp
+++ change-namespace/ChangeNamespace.cpp
@@ -322,7 +322,7 @@
   Finder->addMatcher(
       typeLoc(IsInMovedNs,
               loc(qualType(hasDeclaration(DeclMatcher.bind("from_decl")))),
-              unless(anyOf(hasParent(typeLoc(loc(qualType(
+              unless(anyOf(hasAncestor(typeLoc(loc(qualType(
                                allOf(hasDeclaration(DeclMatcher),
                                      unless(templateSpecializationType())))))),
                            hasParent(nestedNameSpecifierLoc()))),
@@ -520,7 +520,13 @@
   // Delete the forward declaration from the code to be moved.
   const auto Deletion =
       createReplacement(Start, End, "", *Result.SourceManager);
-  addOrMergeReplacement(Deletion, &FileToReplacements[Deletion.getFilePath()]);
+  auto Err = FileToReplacements[Deletion.getFilePath()].add(Deletion);
+  if (Err) {
+    llvm::errs() << "Failed to add replacements: " << Deletion.toString()
+                 << "\n"
+                 << llvm::toString(std::move(Err)) << "\n";
+    assert(false);
+  }
   llvm::StringRef Code = Lexer::getSourceText(
       CharSourceRange::getTokenRange(
           Result.SourceManager->getSpellingLoc(Start),
@@ -606,7 +612,12 @@
   if (NestedName == ReplaceName)
     return;
   auto R = createReplacement(Start, End, ReplaceName, *Result.SourceManager);
-  addOrMergeReplacement(R, &FileToReplacements[R.getFilePath()]);
+  auto Err = FileToReplacements[R.getFilePath()].add(R);
+  if (Err) {
+    llvm::errs() << "Failed to add replacements: " << R.toString() << "\n"
+                 << llvm::toString(std::move(Err)) << "\n";
+    assert(false);
+  }
 }
 
 // Replace the [Start, End] of `Type` with the shortest qualified name when the
@@ -667,7 +678,12 @@
   // Use fully qualified name in UsingDecl for now.
   auto R = createReplacement(Start, End, "using ::" + TargetDeclName,
                              *Result.SourceManager);
-  addOrMergeReplacement(R, &FileToReplacements[R.getFilePath()]);
+  auto Err = FileToReplacements[R.getFilePath()].add(R);
+  if (Err) {
+    llvm::errs() << "Failed to add replacements: " << R.toString() << "\n"
+                 << llvm::toString(std::move(Err)) << "\n";
+    assert(false);
+  }
 }
 
 void ChangeNamespaceTool::onEndOfTranslationUnit() {
Index: unittests/change-namespace/ChangeNamespaceTests.cpp
===================================================================
--- unittests/change-namespace/ChangeNamespaceTests.cpp
+++ unittests/change-namespace/ChangeNamespaceTests.cpp
@@ -1005,6 +1005,35 @@
   EXPECT_EQ(format(Expected), runChangeNamespaceOnCode(Code));
 }
 
+TEST_F(ChangeNamespaceTest, DerivedClassWithConstructors) {
+  std::string Code =
+      "namespace nx { namespace ny { class X { public: X(int i) {} }; } }\n"
+      "namespace na {\n"
+      "namespace nb {\n"
+      "class A : public nx::ny::X {\n"
+      "public:\n"
+      "  A() : X::X(0) {}\n"
+      "  A(int i);\n"
+      "};\n"
+      "A::A(int i) : X::X(i) {}\n"
+      "} // namespace nb\n"
+      "} // namespace na\n";
+  std::string Expected =
+      "namespace nx { namespace ny { class X { public: X(int i) {} }; } }\n"
+      "\n\n"
+      "namespace x {\n"
+      "namespace y {\n"
+      "class A : public nx::ny::X {\n"
+      "public:\n"
+      "  A() : X::X(0) {}\n"
+      "  A(int i);\n"
+      "};\n"
+      "A::A(int i) : X::X(i) {}\n"
+      "} // namespace y\n"
+      "} // namespace x\n";
+  EXPECT_EQ(format(Expected), runChangeNamespaceOnCode(Code));
+}
+
 } // anonymous namespace
 } // namespace change_namespace
 } // namespace clang