diff --git a/include/clang/Basic/DiagnosticLexKinds.td b/include/clang/Basic/DiagnosticLexKinds.td
index 8d6983122d..bd10642534 100644
--- a/include/clang/Basic/DiagnosticLexKinds.td
+++ b/include/clang/Basic/DiagnosticLexKinds.td
@@ -214,6 +214,10 @@ def ext_stdc_pragma_syntax :
 def ext_stdc_pragma_syntax_eom :
    ExtWarn<"expected end of macro in STDC pragma">,
    InGroup<UnknownPragmas>;
+def warn_stdc_fenv_access_not_supported :
+   ExtWarn<"pragma STDC FENV_ACCESS ON is not supported, ignoring pragma">,
+   InGroup<UnknownPragmas>;
+
 def err_pragma_comment_unknown_kind : Error<"unknown kind of pragma comment">;
 def err_defined_macro_name : Error<"'defined' cannot be used as a macro name">;
 def err_paste_at_start : Error<
diff --git a/lib/Lex/Pragma.cpp b/lib/Lex/Pragma.cpp
index d30ff3c289..0dc093fd74 100644
--- a/lib/Lex/Pragma.cpp
+++ b/lib/Lex/Pragma.cpp
@@ -560,7 +560,8 @@ struct PragmaSTDC_FP_CONTRACTHandler : public PragmaHandler {
 struct PragmaSTDC_FENV_ACCESSHandler : public PragmaHandler {
   PragmaSTDC_FENV_ACCESSHandler(const IdentifierInfo *ID) : PragmaHandler(ID) {}
   virtual void HandlePragma(Preprocessor &PP, Token &Tok) {
-    LexOnOffSwitch(PP);
+    if (LexOnOffSwitch(PP) == STDC_ON)
+      PP.Diag(Tok, diag::warn_stdc_fenv_access_not_supported);
   }
 };
   
diff --git a/test/Preprocessor/pragma_unknown.c b/test/Preprocessor/pragma_unknown.c
index d2738e5c7c..16bf43b3f4 100644
--- a/test/Preprocessor/pragma_unknown.c
+++ b/test/Preprocessor/pragma_unknown.c
@@ -10,7 +10,7 @@
 #pragma STDC FP_CONTRACT DEFAULT
 #pragma STDC FP_CONTRACT IN_BETWEEN  // expected-warning {{expected 'ON' or 'OFF' or 'DEFAULT' in pragma}}
 
-#pragma STDC FENV_ACCESS ON
+#pragma STDC FENV_ACCESS ON          // expected-warning {{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
 #pragma STDC FENV_ACCESS OFF
 #pragma STDC FENV_ACCESS DEFAULT
 #pragma STDC FENV_ACCESS IN_BETWEEN   // expected-warning {{expected 'ON' or 'OFF' or 'DEFAULT' in pragma}}