diff --git a/clang/lib/Tooling/Transformer/Transformer.cpp b/clang/lib/Tooling/Transformer/Transformer.cpp
--- a/clang/lib/Tooling/Transformer/Transformer.cpp
+++ b/clang/lib/Tooling/Transformer/Transformer.cpp
@@ -12,6 +12,7 @@
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Tooling/Refactoring/AtomicChange.h"
 #include "llvm/Support/Error.h"
+#include <map>
 #include <utility>
 #include <vector>
 
@@ -45,28 +46,39 @@
     return;
   }
 
-  // Record the results in the AtomicChange, anchored at the location of the
-  // first change.
-  AtomicChange AC(*Result.SourceManager,
-                  (*Transformations)[0].Range.getBegin());
+  // Group the transformations, by file, into AtomicChanges, each anchored by
+  // the location of the first change in that file.
+  std::map<FileID, AtomicChange> ChangesByFileID;
   for (const auto &T : *Transformations) {
+    auto ID = Result.SourceManager->getFileID(T.Range.getBegin());
+    auto Iter = ChangesByFileID
+                    .emplace(ID, AtomicChange(*Result.SourceManager,
+                                              T.Range.getBegin()))
+                    .first;
+    auto &AC = Iter->second;
     if (auto Err = AC.replace(*Result.SourceManager, T.Range, T.Replacement)) {
       Consumer(std::move(Err));
       return;
     }
   }
 
-  for (const auto &I : Case.AddedIncludes) {
-    auto &Header = I.first;
-    switch (I.second) {
-    case transformer::IncludeFormat::Quoted:
-      AC.addHeader(Header);
-      break;
-    case transformer::IncludeFormat::Angled:
-      AC.addHeader((llvm::Twine("<") + Header + ">").str());
-      break;
+  for (auto &IDChangePair : ChangesByFileID) {
+    auto &AC = IDChangePair.second;
+    // FIXME: this will add includes to *all* changed files, which may not be
+    // the intent. We should upgrade the representation to allow associating
+    // headers with specific edits.
+    for (const auto &I : Case.AddedIncludes) {
+      auto &Header = I.first;
+      switch (I.second) {
+      case transformer::IncludeFormat::Quoted:
+        AC.addHeader(Header);
+        break;
+      case transformer::IncludeFormat::Angled:
+        AC.addHeader((llvm::Twine("<") + Header + ">").str());
+        break;
+      }
     }
-  }
 
-  Consumer(std::move(AC));
+    Consumer(std::move(AC));
+  }
 }
diff --git a/clang/unittests/Tooling/TransformerTest.cpp b/clang/unittests/Tooling/TransformerTest.cpp
--- a/clang/unittests/Tooling/TransformerTest.cpp
+++ b/clang/unittests/Tooling/TransformerTest.cpp
@@ -817,4 +817,46 @@
                "Matcher must be.*node matcher");
 }
 #endif
+
+// Edits are able to span multiple files; in this case, a header and an
+// implementation file.
+TEST_F(TransformerTest, MultipleFiles) {
+  std::string Header = R"cc(void RemoveThisFunction();)cc";
+  std::string Source = R"cc(#include "input.h"
+                            void RemoveThisFunction();)cc";
+  Transformer T(
+      makeRule(functionDecl(hasName("RemoveThisFunction")), changeTo(cat(""))),
+      consumer());
+  T.registerMatchers(&MatchFinder);
+  auto Factory = newFrontendActionFactory(&MatchFinder);
+  EXPECT_TRUE(runToolOnCodeWithArgs(
+      Factory->create(), Source, std::vector<std::string>(), "input.cc",
+      "clang-tool", std::make_shared<PCHContainerOperations>(),
+      {{"input.h", Header}}));
+
+  std::sort(Changes.begin(), Changes.end(),
+            [](const AtomicChange &L, const AtomicChange &R) {
+              return L.getFilePath() < R.getFilePath();
+            });
+
+  ASSERT_EQ(Changes[0].getFilePath(), "./input.h");
+  EXPECT_THAT(Changes[0].getInsertedHeaders(), IsEmpty());
+  EXPECT_THAT(Changes[0].getRemovedHeaders(), IsEmpty());
+  llvm::Expected<std::string> UpdatedCode =
+      clang::tooling::applyAllReplacements(Header,
+                                           Changes[0].getReplacements());
+  ASSERT_TRUE(static_cast<bool>(UpdatedCode))
+      << "Could not update code: " << llvm::toString(UpdatedCode.takeError());
+  EXPECT_EQ(format(*UpdatedCode), format(R"cc(;)cc"));
+
+  ASSERT_EQ(Changes[1].getFilePath(), "input.cc");
+  EXPECT_THAT(Changes[1].getInsertedHeaders(), IsEmpty());
+  EXPECT_THAT(Changes[1].getRemovedHeaders(), IsEmpty());
+  UpdatedCode = clang::tooling::applyAllReplacements(
+      Source, Changes[1].getReplacements());
+  ASSERT_TRUE(static_cast<bool>(UpdatedCode))
+      << "Could not update code: " << llvm::toString(UpdatedCode.takeError());
+  EXPECT_EQ(format(*UpdatedCode), format(R"cc(#include "input.h"
+                        ;)cc"));
+}
 } // namespace