diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index d8c3744..1c396bd 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -42,7 +42,7 @@
   // Compute the initial Darwin version based on the host.
   bool HadExtra;
   std::string OSName = Triple.getOSName();
-  if (!Driver::GetReleaseVersion(&OSName[6],
+  if (!Driver::GetReleaseVersion(&OSName.c_str()[6],
                                  DarwinVersion[0], DarwinVersion[1],
                                  DarwinVersion[2], HadExtra))
     getDriver().Diag(clang::diag::err_drv_invalid_darwin_version) << OSName;