diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -1647,6 +1647,7 @@
   /// Only common bits are stored here. Additional uncommon bits are stored
   /// in a trailing object after FunctionProtoType.
   class FunctionTypeBitfields {
+    friend class FunctionNoProtoType;
     friend class FunctionProtoType;
     friend class FunctionType;
 
@@ -3942,7 +3943,9 @@
                      Result->getDependence() &
                          ~(TypeDependence::DependentInstantiation |
                            TypeDependence::UnexpandedPack),
-                     Info) {}
+                     Info) {
+    FunctionTypeBits.FastTypeQuals = 0;
+  }
 
 public:
   // No additional state past what FunctionType provides.
diff --git a/clang/unittests/AST/DeclTest.cpp b/clang/unittests/AST/DeclTest.cpp
--- a/clang/unittests/AST/DeclTest.cpp
+++ b/clang/unittests/AST/DeclTest.cpp
@@ -354,3 +354,24 @@
 
   EXPECT_TRUE(getFooValue->isInlined());
 }
+
+TEST(Decl, NoProtoFunctionDeclAttributes) {
+  llvm::Annotations Code(R"(
+    void f();
+    )");
+
+  auto AST = tooling::buildASTFromCodeWithArgs(
+      Code.code(),
+      /*Args=*/{"-target", "i386-apple-darwin", "-x", "objective-c"});
+  ASTContext &Ctx = AST->getASTContext();
+
+  auto *f = selectFirst<FunctionDecl>(
+      "f", match(functionDecl(hasName("f")).bind("f"), Ctx));
+
+  const auto *FPT = f->getType()->getAs<FunctionNoProtoType>();
+
+  // Functions without prototypes always have 0 initialized qualifiers
+  EXPECT_FALSE(FPT->isConst());
+  EXPECT_FALSE(FPT->isVolatile());
+  EXPECT_FALSE(FPT->isRestrict());
+}