diff --git a/clang/include/clang/Sema/SemaConcept.h b/clang/include/clang/Sema/SemaConcept.h
--- a/clang/include/clang/Sema/SemaConcept.h
+++ b/clang/include/clang/Sema/SemaConcept.h
@@ -43,11 +43,23 @@
       return false;
 
     for (unsigned I = 0, S = ParameterMapping->size(); I < S; ++I) {
+      auto LHS =
+          C.getCanonicalTemplateArgument((*ParameterMapping)[I].getArgument());
+      auto RHS = C.getCanonicalTemplateArgument(
+          (*Other.ParameterMapping)[I].getArgument());
+      // QualType of constrained template template parameter is not the same as
+      // its tailing version, so give it a pass here.
+      if (LHS.getKind() == TemplateArgument::Type &&
+          RHS.getKind() == TemplateArgument::Type &&
+	  isa<TemplateTypeParmType>(LHS.getAsType()) &&
+	  isa<TemplateTypeParmType>(RHS.getAsType())) {
+        if (cast<TemplateTypeParmType>(LHS.getAsType())->getIndex() ==
+            cast<TemplateTypeParmType>(RHS.getAsType())->getIndex())
+          continue;
+      }
       llvm::FoldingSetNodeID IDA, IDB;
-      C.getCanonicalTemplateArgument((*ParameterMapping)[I].getArgument())
-          .Profile(IDA, C);
-      C.getCanonicalTemplateArgument((*Other.ParameterMapping)[I].getArgument())
-          .Profile(IDB, C);
+      LHS.Profile(IDA, C);
+      RHS.Profile(IDB, C);
       if (IDA != IDB)
         return false;
     }
diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -874,27 +874,39 @@
 /// template parameters.
 ///
 ///       type-parameter:    [C++ temp.param]
-///         'template' '<' template-parameter-list '>' type-parameter-key
-///                  ...[opt] identifier[opt]
-///         'template' '<' template-parameter-list '>' type-parameter-key
-///                  identifier[opt] = id-expression
+///         template-head type-parameter-key ...[opt] identifier[opt]
+///         template-head type-parameter-key identifier[opt] = id-expression
 ///       type-parameter-key:
 ///         'class'
 ///         'typename'       [C++1z]
-NamedDecl *
-Parser::ParseTemplateTemplateParameter(unsigned Depth, unsigned Position) {
+///       template-head:     [C++2a]
+///         'template' '<' template-parameter-list '>'
+///             requires-clause[opt]
+NamedDecl *Parser::ParseTemplateTemplateParameter(unsigned Depth,
+                                                  unsigned Position) {
   assert(Tok.is(tok::kw_template) && "Expected 'template' keyword");
 
   // Handle the template <...> part.
   SourceLocation TemplateLoc = ConsumeToken();
   SmallVector<NamedDecl*,8> TemplateParams;
   SourceLocation LAngleLoc, RAngleLoc;
+  ExprResult OptionalRequiresClauseConstraintER;
   {
     MultiParseScope TemplateParmScope(*this);
     if (ParseTemplateParameters(TemplateParmScope, Depth + 1, TemplateParams,
                                 LAngleLoc, RAngleLoc)) {
       return nullptr;
     }
+    if (TryConsumeToken(tok::kw_requires)) {
+      OptionalRequiresClauseConstraintER =
+          Actions.ActOnRequiresClause(ParseConstraintLogicalOrExpression(
+              /*IsTrailingRequiresClause=*/false));
+      if (!OptionalRequiresClauseConstraintER.isUsable()) {
+        SkipUntil(tok::comma, tok::greater, tok::greatergreater,
+                  StopAtSemi | StopBeforeMatch);
+        return nullptr;
+      }
+    }
   }
 
   // Provide an ExtWarn if the C++1z feature of using 'typename' here is used.
@@ -956,11 +968,9 @@
   if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
     DiagnoseMisplacedEllipsis(EllipsisLoc, NameLoc, AlreadyHasEllipsis, true);
 
-  TemplateParameterList *ParamList =
-    Actions.ActOnTemplateParameterList(Depth, SourceLocation(),
-                                       TemplateLoc, LAngleLoc,
-                                       TemplateParams,
-                                       RAngleLoc, nullptr);
+  TemplateParameterList *ParamList = Actions.ActOnTemplateParameterList(
+      Depth, SourceLocation(), TemplateLoc, LAngleLoc, TemplateParams,
+      RAngleLoc, OptionalRequiresClauseConstraintER.get());
 
   // Grab a default argument (if available).
   // Per C++0x [basic.scope.pdecl]p9, we parse the default argument before
diff --git a/clang/test/CXX/temp/temp.arg/temp.arg.template/p3-2a.cpp b/clang/test/CXX/temp/temp.arg/temp.arg.template/p3-2a.cpp
--- a/clang/test/CXX/temp/temp.arg/temp.arg.template/p3-2a.cpp
+++ b/clang/test/CXX/temp/temp.arg/temp.arg.template/p3-2a.cpp
@@ -1,22 +1,27 @@
 // RUN:  %clang_cc1 -std=c++2a -frelaxed-template-template-args -verify %s
 
-template<typename T> concept C = T::f();
-// expected-note@-1{{similar constraint}}
+template<typename T> concept C = T::f(); // #C
 template<typename T> concept D = C<T> && T::g();
-template<typename T> concept F = T::f();
-// expected-note@-1{{similar constraint expressions not considered equivalent}}
-template<template<C> class P> struct S1 { }; // expected-note 2{{'P' declared here}}
+template<typename T> concept F = T::f(); // #F
+template<template<C> class P> struct S1 { }; // #S1
 
 template<C> struct X { };
-
-template<D> struct Y { }; // expected-note{{'Y' declared here}}
+template<D> struct Y { }; // #Y
 template<typename T> struct Z { };
-template<F> struct W { }; // expected-note{{'W' declared here}}
+template<F> struct W { }; // #W
 
 S1<X> s11;
-S1<Y> s12; // expected-error{{template template argument 'Y' is more constrained than template template parameter 'P'}}
+S1<Y> s12;
+// expected-error@-1 {{template template argument 'Y' is more constrained than template template parameter 'P'}}
+// expected-note@#S1 {{'P' declared here}}
+// expected-note@#Y {{'Y' declared here}}
 S1<Z> s13;
-S1<W> s14; // expected-error{{template template argument 'W' is more constrained than template template parameter 'P'}}
+S1<W> s14;
+// expected-error@-1 {{template template argument 'W' is more constrained than template template parameter 'P'}}
+// expected-note@#S1 {{'P' declared here}}
+// expected-note@#W {{'W' declared here}}
+// expected-note@#F {{similar constraint expressions not considered equivalent}}
+// expected-note@#C {{similar constraint}}
 
 template<template<typename> class P> struct S2 { };
 
@@ -32,3 +37,27 @@
 
 using s31 = S3<N>;
 using s32 = S3<Z>;
+
+template<template<typename T> requires C<T> class P> struct S4 { }; // #S4
+
+S4<X> s41;
+S4<Y> s42;
+// expected-error@-1 {{template template argument 'Y' is more constrained than template template parameter 'P'}}
+// expected-note@#S4 {{'P' declared here}}
+// expected-note@#Y {{'Y' declared here}}
+S4<Z> s43;
+S4<W> s44;
+// expected-error@-1 {{template template argument 'W' is more constrained than template template parameter 'P'}}
+// expected-note@#S4 {{'P' declared here}}
+// expected-note@#W {{'W' declared here}}
+// expected-note@#F {{similar constraint expressions not considered equivalent}}
+// expected-note@#C {{similar constraint}}
+
+template<template<typename T> requires C<T> typename U> struct S5 {
+  template<typename T> static U<T> V;
+};
+
+struct Nothing {};
+
+// FIXME: Wait the standard to clarify the intent.
+template<> template<> Z<Nothing> S5<Z>::V<Nothing>;
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -59,11 +59,10 @@
     x.operator()<false>(); // expected-error {{no matching member function}}
   }
 
-  // FIXME: This is valid under P0857R0.
   template<typename T> concept C = true;
-  template<template<typename T> requires C<T> typename U> struct X {}; // expected-error {{requires 'class'}} expected-error 0+{{}}
+  template<template<typename T> requires C<T> typename U> struct X {};
   template<typename T> requires C<T> struct Y {};
-  X<Y> xy; // expected-error {{no template named 'X'}}
+  X<Y> xy;
 }
 
 namespace PR50306 {
diff --git a/clang/www/cxx_status.html b/clang/www/cxx_status.html
--- a/clang/www/cxx_status.html
+++ b/clang/www/cxx_status.html
@@ -912,11 +912,7 @@
     </tr>
       <tr> <!-- from Albuquerque -->
         <td><a href="https://wg21.link/p0857r0">P0857R0</a></td>
-        <td class="partial" align="center">
-          <details><summary>Partial</summary>
-            Constraining template template parameters is not yet supported.
-          </details>
-        </td>
+        <td class="unreleased" align="center">Clang 16</td>
       </tr>
       <tr> <!-- from San Diego -->
         <td><a href="https://wg21.link/p1084r2">P1084R2</a></td>