diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 8b159f0..04d4d44 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1180,6 +1180,15 @@
     }
   }
 
+  // Diagnose misuse of /o.
+  if (Arg *A = Args.getLastArg(options::OPT__SLASH_o)) {
+    if (A->getValue()[0] == '\0') {
+      // It has to have a value.
+      Diag(clang::diag::err_drv_missing_argument) << A->getSpelling() << 1;
+      Args.eraseArg(options::OPT__SLASH_o);
+    }
+  }
+
   // Construct the actions to perform.
   ActionList LinkerInputs;
 
@@ -1651,7 +1660,8 @@
     assert(AtTopLevel && isa<PreprocessJobAction>(JA));
     StringRef BaseName = llvm::sys::path::filename(BaseInput);
     StringRef NameArg;
-    if (Arg *A = C.getArgs().getLastArg(options::OPT__SLASH_Fi))
+    if (Arg *A = C.getArgs().getLastArg(options::OPT__SLASH_Fi,
+                                        options::OPT__SLASH_o))
       NameArg = A->getValue();
     return C.addResultFile(MakeCLOutputFilename(C.getArgs(), NameArg, BaseName,
                                                 types::TY_PP_C), &JA);
@@ -1698,15 +1708,17 @@
   const char *NamedOutput;
 
   if (JA.getType() == types::TY_Object &&
-      C.getArgs().hasArg(options::OPT__SLASH_Fo)) {
-    // The /Fo flag decides the object filename.
-    StringRef Val = C.getArgs().getLastArg(options::OPT__SLASH_Fo)->getValue();
+      C.getArgs().hasArg(options::OPT__SLASH_Fo, options::OPT__SLASH_o)) {
+    // The /Fo or /o flag decides the object filename.
+    StringRef Val = C.getArgs().getLastArg(options::OPT__SLASH_Fo,
+                                           options::OPT__SLASH_o)->getValue();
     NamedOutput = MakeCLOutputFilename(C.getArgs(), Val, BaseName,
                                        types::TY_Object);
   } else if (JA.getType() == types::TY_Image &&
-             C.getArgs().hasArg(options::OPT__SLASH_Fe)) {
-    // The /Fe flag names the linked file.
-    StringRef Val = C.getArgs().getLastArg(options::OPT__SLASH_Fe)->getValue();
+             C.getArgs().hasArg(options::OPT__SLASH_Fe, options::OPT__SLASH_o)) {
+    // The /Fe or /o flag names the linked file.
+    StringRef Val = C.getArgs().getLastArg(options::OPT__SLASH_Fe,
+                                           options::OPT__SLASH_o)->getValue();
     NamedOutput = MakeCLOutputFilename(C.getArgs(), Val, BaseName,
                                        types::TY_Image);
   } else if (JA.getType() == types::TY_Image) {