Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -5669,9 +5669,6 @@
       std::find(Features.begin(), Features.end(), "+soft-float");
     if (it != Features.end())
       Features.erase(it);
-    it = std::find(Features.begin(), Features.end(), "+nan2008");
-    if (it != Features.end())
-      Features.erase(it);
 
     setDescriptionString();
 
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -1037,8 +1037,14 @@
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_mnan_EQ)) {
-    if (StringRef(A->getValue()) == "2008")
+    StringRef Val = StringRef(A->getValue());
+    if (Val == "2008")
       Features.push_back("+nan2008");
+    else if (Val == "legacy")
+      Features.push_back("-nan2008");
+    else
+      D.Diag(diag::err_drv_unsupported_option_argument)
+          << A->getOption().getName() << Val;
   }
 
   AddTargetFeature(Args, Features, options::OPT_msingle_float,
Index: test/Driver/mips-features.c
===================================================================
--- test/Driver/mips-features.c
+++ test/Driver/mips-features.c
@@ -72,6 +72,18 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NOMFP64 %s
 // CHECK-NOMFP64: "-target-feature" "-fp64"
 //
+// -mnan=2008
+// RUN: %clang -target mips-linux-gnu -### -c %s \
+// RUN:     -mnan=legacy -mnan=2008 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NAN2008 %s
+// CHECK-NAN2008: "-target-feature" "+nan2008"
+//
+// -mnan=legacy
+// RUN: %clang -target mips-linux-gnu -### -c %s \
+// RUN:     -mnan=2008 -mnan=legacy 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NANLEGACY %s
+// CHECK-NANLEGACY: "-target-feature" "-nan2008"
+//
 // -mxgot
 // RUN: %clang -target mips-linux-gnu -### -c %s \
 // RUN:     -mno-xgot -mxgot 2>&1 \