diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 954ec8d..223576e 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1139,6 +1139,10 @@
     else if (A->getOption().matches(options::OPT_O) &&
              A->getValue(Args)[0] == '\0')
       CmdArgs.push_back("-O2");
+    else if (A->getOption().matches(options::OPT_O) &&
+             A->getValue(Args)[0] == 'z' &&
+             A->getValue(Args)[1] == '\0')
+      CmdArgs.push_back("-Os");
     else
       A->render(Args, CmdArgs);
   }