Index: clang/lib/Lex/PPMacroExpansion.cpp
===================================================================
--- clang/lib/Lex/PPMacroExpansion.cpp
+++ clang/lib/Lex/PPMacroExpansion.cpp
@@ -1693,8 +1693,14 @@
       [this](Token &Tok, bool &HasLexedNextToken) -> int {
         IdentifierInfo *II = ExpectFeatureIdentifierInfo(Tok, *this,
                                            diag::err_feature_check_malformed);
-        return II ? hasAttribute(AttrSyntax::Declspec, nullptr, II,
-                                 getTargetInfo(), getLangOpts()) : 0;
+        if (II) {
+          const LangOptions &LangOpts = getLangOpts();
+          return LangOpts.DeclSpecKeyword &&
+                 hasAttribute(AttrSyntax::Declspec, nullptr, II,
+                              getTargetInfo(), LangOpts);
+        }
+
+        return false;
       });
   } else if (II == Ident__has_cpp_attribute ||
              II == Ident__has_c_attribute) {
Index: clang/test/Preprocessor/has_declspec_attribute.c
===================================================================
--- /dev/null
+++ clang/test/Preprocessor/has_declspec_attribute.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -E -P %s -o - | FileCheck %s --check-prefix=CHECK
+// RUN: %clang_cc1 -triple i386-unknown-unknown -fdeclspec -E -P %s -o - | FileCheck %s --check-prefix=ENABLED
+// RUN: %clang_cc1 -triple i386-unknown-unknown -fms-extensions -E -P %s -o - | FileCheck %s --check-prefix=ENABLED
+
+// Check that __has_declspec_attribute() always returns 0 if declspec
+// attributes have not been explicitly enabled.
+
+#define DECLSPEC(x) x: __has_declspec_attribute(x)
+// CHECK: noreturn: 0
+// ENABLED: noreturn: 1
+DECLSPEC(noreturn)