diff --git a/Driver/PrintPreprocessedOutput.cpp b/Driver/PrintPreprocessedOutput.cpp
index 2a363f8..b903008 100644
--- a/Driver/PrintPreprocessedOutput.cpp
+++ b/Driver/PrintPreprocessedOutput.cpp
@@ -500,7 +500,7 @@
   
   // Open the output buffer.
   std::string Err;
-  llvm::raw_fd_ostream OS(OutFile.c_str(), Err);
+  llvm::raw_fd_ostream OS(OutFile.empty() ? "-" : OutFile.c_str(), Err);
   if (!Err.empty()) {
     fprintf(stderr, "%s\n", Err.c_str());
     exit(1);