diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index b0f9b317a020..8b3da909dd11 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -684,8 +684,6 @@ def err_attribute_requires_arguments : Error<
   "parentheses must be omitted if %0 attribute's argument list is empty">;
 def err_cxx11_attribute_forbids_ellipsis : Error<
   "attribute %0 cannot be used as an attribute pack">;
-def err_cxx11_attribute_repeated : Error<
-  "attribute %0 cannot appear multiple times in an attribute specifier">;
 def warn_cxx14_compat_using_attribute_ns : Warning<
   "default scope specifier for attributes is incompatible with C++ standards "
   "before C++17">, InGroup<CXXPre17Compat>, DefaultIgnore;
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index e1d29f555f42..bc59b4178257 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -4260,13 +4260,6 @@ void Parser::ParseCXX11AttributeSpecifier(ParsedAttributes &attrs,
       }
     }
 
-    bool StandardAttr = IsBuiltInOrStandardCXX11Attribute(AttrName, ScopeName);
-
-    if (StandardAttr &&
-        !SeenAttrs.insert(std::make_pair(AttrName, AttrLoc)).second)
-      Diag(AttrLoc, diag::err_cxx11_attribute_repeated)
-          << AttrName << SourceRange(SeenAttrs[AttrName]);
-
     // Parse attribute arguments
     if (Tok.is(tok::l_paren))
       AttrParsed = ParseCXX11AttributeArgs(AttrName, AttrLoc, attrs, endLoc,
diff --git a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
index 6cf27af3230b..424b159667c3 100644
--- a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -verify -std=c++11 %s
 
-[[carries_dependency, carries_dependency]] int m1(); // expected-error {{attribute 'carries_dependency' cannot appear multiple times in an attribute specifier}}
+[[carries_dependency, carries_dependency]] int m1(); // ok
 [[carries_dependency]] [[carries_dependency]] int m2(); // ok
 [[carries_dependency()]] int m3(); // expected-error {{attribute 'carries_dependency' cannot have an argument list}}
 
diff --git a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.fallthrough/p1.cpp b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.fallthrough/p1.cpp
index 22815bbde9db..675ab3e089b8 100644
--- a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.fallthrough/p1.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.fallthrough/p1.cpp
@@ -61,7 +61,7 @@ void g() {
     return;
 
   case 0:
-    [[fallthrough, fallthrough]]; // expected-error {{multiple times}}
+    [[fallthrough, fallthrough]]; // ok
   case 1:
     [[fallthrough(0)]]; // expected-error {{argument list}}
   case 2:
diff --git a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p1.cpp b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p1.cpp
index 982f18f1e8cd..142d4d6f369f 100644
--- a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p1.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p1.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -fsyntax-only -std=c++2a -verify %s
 
 struct [[nodiscard]] S1 {}; // ok
-struct [[nodiscard, nodiscard]] S2 {}; // expected-error {{attribute 'nodiscard' cannot appear multiple times in an attribute specifier}}
+struct [[nodiscard, nodiscard]] S2 {}; // ok
 struct [[nodiscard("Wrong")]] S3 {};
 
 [[nodiscard]] int f();
diff --git a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.noreturn/p1.cpp b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.noreturn/p1.cpp
index d92356c1ec0b..49c1106b51a5 100644
--- a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.noreturn/p1.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.noreturn/p1.cpp
@@ -14,7 +14,7 @@ template <typename T> void a4 [[noreturn]] () { return; } // expected-warning {{
                                                           // expected-warning@-1 {{function 'a4<long>' declared 'noreturn' should not return}}
 void a4_test() { a4<long>(); } // expected-note {{in instantiation of function template specialization 'a4<long>' requested here}}
 
-[[noreturn, noreturn]] void b() { throw 0; } // expected-error {{attribute 'noreturn' cannot appear multiple times in an attribute specifier}}
+[[noreturn, noreturn]] void b() { throw 0; } // ok
 [[noreturn]] [[noreturn]] void b2() { throw 0; } // ok
 
 [[noreturn()]] void c(); // expected-error {{attribute 'noreturn' cannot have an argument list}}
diff --git a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.unused/p1.cpp b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.unused/p1.cpp
index 6c9b8a75cb04..2cee3cbcdf8a 100644
--- a/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.unused/p1.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.unused/p1.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -Wunused -std=c++1z -verify %s
 
 struct [[maybe_unused]] S1 {}; // ok
-struct [[maybe_unused, maybe_unused]] S2 {}; // expected-error {{attribute 'maybe_unused' cannot appear multiple times in an attribute specifier}}
+struct [[maybe_unused, maybe_unused]] S2 {}; // ok
 struct [[maybe_unused("Wrong")]] S3 {}; // expected-error {{'maybe_unused' cannot have an argument list}}
diff --git a/clang/test/Sema/c2x-fallthrough.c b/clang/test/Sema/c2x-fallthrough.c
index e5508e0a10f1..baa62aa8f140 100644
--- a/clang/test/Sema/c2x-fallthrough.c
+++ b/clang/test/Sema/c2x-fallthrough.c
@@ -65,7 +65,7 @@ void g(void) {
     return;
 
   case 0:
-    [[fallthrough, fallthrough]]; // expected-error {{multiple times}}
+    [[fallthrough, fallthrough]]; // ok
   case 1:
     [[fallthrough(0)]]; // expected-error {{argument list}}
   case 2:
diff --git a/clang/test/Sema/c2x-maybe_unused-errors.c b/clang/test/Sema/c2x-maybe_unused-errors.c
index 5d3eb4d47a6e..72cefd10291a 100644
--- a/clang/test/Sema/c2x-maybe_unused-errors.c
+++ b/clang/test/Sema/c2x-maybe_unused-errors.c
@@ -3,7 +3,7 @@
 struct [[maybe_unused]] S1 { // ok
   int a [[maybe_unused]];
 };
-struct [[maybe_unused, maybe_unused]] S2 { // expected-error {{attribute 'maybe_unused' cannot appear multiple times in an attribute specifier}}
+struct [[maybe_unused, maybe_unused]] S2 { // ok
   int a;
 };
 struct [[maybe_unused("Wrong")]] S3 { // expected-error {{'maybe_unused' cannot have an argument list}}
diff --git a/clang/test/Sema/c2x-nodiscard.c b/clang/test/Sema/c2x-nodiscard.c
index f62ba27c12a1..812421757d34 100644
--- a/clang/test/Sema/c2x-nodiscard.c
+++ b/clang/test/Sema/c2x-nodiscard.c
@@ -3,7 +3,7 @@
 struct [[nodiscard]] S1 { // ok
   int i;
 };
-struct [[nodiscard, nodiscard]] S2 { // expected-error {{attribute 'nodiscard' cannot appear multiple times in an attribute specifier}}
+struct [[nodiscard, nodiscard]] S2 { // ok
   int i;
 };
 struct [[nodiscard("Wrong")]] S3 { // FIXME: may need an extension warning.
diff --git a/clang/test/SemaCXX/cxx2a-no-unique-address.cpp b/clang/test/SemaCXX/cxx2a-no-unique-address.cpp
index 107466e33145..44d6d3acddde 100644
--- a/clang/test/SemaCXX/cxx2a-no-unique-address.cpp
+++ b/clang/test/SemaCXX/cxx2a-no-unique-address.cpp
@@ -10,8 +10,8 @@ struct [[no_unique_address]] S { // expected-error {{only applies to non-bit-fie
   [[no_unique_address]] static void sf(); // expected-error {{only applies to non-bit-field non-static data members}} unsupported-warning {{unknown}}
   [[no_unique_address]] int b : 3; // expected-error {{only applies to non-bit-field non-static data members}} unsupported-warning {{unknown}}
 
-  [[no_unique_address, no_unique_address]] int duplicated; // expected-error {{cannot appear multiple times}}
-  // unsupported-error@-1 {{cannot appear multiple times}} unsupported-warning@-1 2{{unknown}}
+  [[no_unique_address, no_unique_address]] int duplicated; // ok
+  // unsupported-warning@-1 2{{unknown}}
   [[no_unique_address]] [[no_unique_address]] int duplicated2; // unsupported-warning 2{{unknown}}
   [[no_unique_address()]] int arglist; // expected-error {{cannot have an argument list}} unsupported-warning {{unknown}}