diff --git a/lib/Frontend/CompilerInstance.cpp b/lib/Frontend/CompilerInstance.cpp
index bc63e98..ace3c5a 100644
--- a/lib/Frontend/CompilerInstance.cpp
+++ b/lib/Frontend/CompilerInstance.cpp
@@ -117,7 +117,7 @@
     // Create the output stream.
     llvm::raw_fd_ostream *FileOS(
       new llvm::raw_fd_ostream(DiagOpts.DiagnosticLogFile.c_str(),
-                               ErrorInfo));
+                               ErrorInfo, llvm::raw_fd_ostream::F_Append));
     if (!ErrorInfo.empty()) {
       Diags.Report(diag::warn_fe_cc_log_diagnostics_failure)
         << DiagOpts.DumpBuildInformation << ErrorInfo;