Index: include-fixer/tool/ClangIncludeFixer.cpp
===================================================================
--- include-fixer/tool/ClangIncludeFixer.cpp
+++ include-fixer/tool/ClangIncludeFixer.cpp
@@ -211,9 +211,13 @@
     tooling::Replacements Replacements =
         clang::include_fixer::createInsertHeaderReplacements(
             Code->getBuffer(), FilePath, Context.Headers[0], InsertStyle);
-    std::string ChangedCode =
+    auto ChangedCode =
         tooling::applyAllReplacements(Code->getBuffer(), Replacements);
-    llvm::outs() << ChangedCode;
+    if (!ChangedCode) {
+      llvm::errs() << llvm::toString(ChangedCode.takeError()) << "\n";
+      return 1;
+    }
+    llvm::outs() << *ChangedCode;
     return 0;
   }
 
@@ -265,9 +269,13 @@
   Diagnostics.setClient(&DiagnosticPrinter, false);
 
   if (STDINMode) {
-    std::string ChangedCode =
+    auto ChangedCode =
         tooling::applyAllReplacements(Code->getBuffer(), Replacements);
-    llvm::outs() << ChangedCode;
+    if (!ChangedCode) {
+      llvm::errs() << llvm::toString(ChangedCode.takeError()) << "\n";
+      return 1;
+    }
+    llvm::outs() << *ChangedCode;
     return 0;
   }
 
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 +122,12 @@
     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.
+    return "";
+  }
+  return *Result;
 }
 
 #define EXPECT_NO_CHANGES(Check, Code)                                         \