Index: include-fixer/IncludeFixer.h
===================================================================
--- include-fixer/IncludeFixer.h
+++ include-fixer/IncludeFixer.h
@@ -68,8 +68,9 @@
 /// \param Header The header being inserted.
 /// \param Style clang-format style being used.
 ///
-/// \return Replacements for inserting and sorting headers.
-tooling::Replacements createInsertHeaderReplacements(
+/// \return Replacements for inserting and sorting headers on success;
+/// otherwise, an llvm::Error carrying llvm::StringError is returned.
+llvm::Expected<tooling::Replacements> createInsertHeaderReplacements(
     StringRef Code, StringRef FilePath, StringRef Header,
     const clang::format::FormatStyle &Style = clang::format::getLLVMStyle());
 
Index: include-fixer/IncludeFixer.cpp
===================================================================
--- include-fixer/IncludeFixer.cpp
+++ include-fixer/IncludeFixer.cpp
@@ -349,7 +349,7 @@
   return !Compiler.getDiagnostics().hasFatalErrorOccurred();
 }
 
-tooling::Replacements
+llvm::Expected<tooling::Replacements>
 createInsertHeaderReplacements(StringRef Code, StringRef FilePath,
                                StringRef Header,
                                const clang::format::FormatStyle &Style) {
@@ -360,8 +360,10 @@
   clang::tooling::Replacements Insertions = {
       tooling::Replacement(FilePath, UINT_MAX, 0, IncludeName)};
 
-  return formatReplacements(
-      Code, cleanupAroundReplacements(Code, Insertions, Style), Style);
+  auto CleanReplaces = cleanupAroundReplacements(Code, Insertions, Style);
+  if (!CleanReplaces)
+    return CleanReplaces;
+  return formatReplacements(Code, *CleanReplaces, Style);
 }
 
 } // namespace include_fixer
Index: include-fixer/tool/ClangIncludeFixer.cpp
===================================================================
--- include-fixer/tool/ClangIncludeFixer.cpp
+++ include-fixer/tool/ClangIncludeFixer.cpp
@@ -209,13 +209,20 @@
       return 1;
     }
 
-    tooling::Replacements Replacements =
-        clang::include_fixer::createInsertHeaderReplacements(
-            Code->getBuffer(), FilePath, Context.getHeaders().front(),
-            InsertStyle);
-    std::string ChangedCode =
-        tooling::applyAllReplacements(Code->getBuffer(), Replacements);
-    llvm::outs() << ChangedCode;
+    auto Replacements = clang::include_fixer::createInsertHeaderReplacements(
+        Code->getBuffer(), FilePath, Context.getHeaders().front(), InsertStyle);
+    if (!Replacements) {
+      errs() << "Failed to create header insertion replacement: "
+             << llvm::toString(Replacements.takeError()) << "\n";
+      return 1;
+    }
+    auto ChangedCode =
+        tooling::applyAllReplacements(Code->getBuffer(), *Replacements);
+    if (!ChangedCode) {
+      llvm::errs() << llvm::toString(ChangedCode.takeError()) << "\n";
+      return 1;
+    }
+    llvm::outs() << *ChangedCode;
     return 0;
   }
 
@@ -250,17 +257,22 @@
     return 1;
   }
 
-  tooling::Replacements Replacements =
-      clang::include_fixer::createInsertHeaderReplacements(
-          /*Code=*/Buffer.get()->getBuffer(), FilePath,
-          Context.getHeaders().front(), InsertStyle);
+  // FIXME: Rank the results and pick the best one instead of the first one.
+  auto Replacements = clang::include_fixer::createInsertHeaderReplacements(
+      /*Code=*/Buffer.get()->getBuffer(), FilePath,
+      Context.getHeaders().front(), InsertStyle);
+  if (!Replacements) {
+    errs() << "Failed to create header insertion replacement: "
+           << llvm::toString(Replacements.takeError()) << "\n";
+    return 1;
+  }
 
   if (!Quiet)
     llvm::errs() << "Added #include" << Context.getHeaders().front();
 
   // Add missing namespace qualifiers to the unidentified symbol.
   if (Context.getSymbolRange().getLength() > 0)
-    Replacements.insert(Context.createSymbolReplacement(FilePath, 0));
+    Replacements->insert(Context.createSymbolReplacement(FilePath, 0));
 
   // Set up a new source manager for applying the resulting replacements.
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts(new DiagnosticOptions);
@@ -270,15 +282,19 @@
   Diagnostics.setClient(&DiagnosticPrinter, false);
 
   if (STDINMode) {
-    std::string ChangedCode =
-        tooling::applyAllReplacements(Code->getBuffer(), Replacements);
-    llvm::outs() << ChangedCode;
+    auto ChangedCode =
+        tooling::applyAllReplacements(Code->getBuffer(), *Replacements);
+    if (!ChangedCode) {
+      llvm::errs() << llvm::toString(ChangedCode.takeError()) << "\n";
+      return 1;
+    }
+    llvm::outs() << *ChangedCode;
     return 0;
   }
 
   // Write replacements to disk.
   Rewriter Rewrites(SM, LangOptions());
-  tooling::applyAllReplacements(Replacements, Rewrites);
+  tooling::applyAllReplacements(*Replacements, Rewrites);
   return Rewrites.overwriteChangedFiles();
 }
 
Index: unittests/clang-tidy/ClangTidyTest.h
===================================================================
--- unittests/clang-tidy/ClangTidyTest.h
+++ unittests/clang-tidy/ClangTidyTest.h
@@ -17,6 +17,7 @@
 #include "clang/Frontend/FrontendActions.h"
 #include "clang/Tooling/Refactoring.h"
 #include "clang/Tooling/Tooling.h"
+#include "llvm/ADT/Optional.h"
 #include <map>
 #include <memory>
 
@@ -121,7 +122,13 @@
     Fixes.insert(Error.Fix.begin(), Error.Fix.end());
   if (Errors)
     *Errors = Context.getErrors();
-  return tooling::applyAllReplacements(Code, Fixes);
+  auto Result = tooling::applyAllReplacements(Code, Fixes);
+  if (!Result) {
+    // FIXME: propogate the error.
+    llvm::consumeError(Result.takeError());
+    return "";
+  }
+  return *Result;
 }
 
 #define EXPECT_NO_CHANGES(Check, Code)                                         \
Index: unittests/include-fixer/IncludeFixerTest.cpp
===================================================================
--- unittests/include-fixer/IncludeFixerTest.cpp
+++ unittests/include-fixer/IncludeFixerTest.cpp
@@ -86,14 +86,17 @@
   runOnCode(&Factory, Code, FakeFileName, ExtraArgs);
   if (FixerContext.getMatchedSymbols().empty())
     return Code;
-  tooling::Replacements Replacements =
-      clang::include_fixer::createInsertHeaderReplacements(
-          Code, FakeFileName, FixerContext.getHeaders().front());
+  auto Replaces = clang::include_fixer::createInsertHeaderReplacements(
+      Code, FakeFileName, FixerContext.getHeaders().front());
+  EXPECT_TRUE(static_cast<bool>(Replaces))
+      << llvm::toString(Replaces.takeError()) << "\n";
+  if (!Replaces)
+    return "";
   clang::RewriterTestContext Context;
   clang::FileID ID = Context.createInMemoryFile(FakeFileName, Code);
   if (FixerContext.getSymbolRange().getLength() > 0)
-    Replacements.insert(FixerContext.createSymbolReplacement(FakeFileName, 0));
-  clang::tooling::applyAllReplacements(Replacements, Context.Rewrite);
+    Replaces->insert(FixerContext.createSymbolReplacement(FakeFileName, 0));
+  clang::tooling::applyAllReplacements(*Replaces, Context.Rewrite);
   return Context.getRewrittenText(ID);
 }