diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -3042,7 +3042,7 @@
   case Char32:
     return "char32_t";
   case NullPtr:
-    return "nullptr_t";
+    return "std::nullptr_t";
   case Overload:
     return "<overloaded function type>";
   case BoundMember:
diff --git a/clang/test/AST/ast-dump-recovery.cpp b/clang/test/AST/ast-dump-recovery.cpp
--- a/clang/test/AST/ast-dump-recovery.cpp
+++ b/clang/test/AST/ast-dump-recovery.cpp
@@ -250,7 +250,7 @@
 // CHECK-NEXT: `-RecoveryExpr {{.*}} '<dependent type>' contains-errors lvalue
 // CHECK-NEXT:   `-InitListExpr
 // CHECK-NEXT:     `-DesignatedInitExpr {{.*}} 'void'
-// CHECK-NEXT:       `-CXXNullPtrLiteralExpr {{.*}} 'nullptr_t'
+// CHECK-NEXT:       `-CXXNullPtrLiteralExpr {{.*}} 'std::nullptr_t'
 struct {
   int& abc;
 } NoCrashOnInvalidInitList = {
diff --git a/clang/test/Analysis/plist-diagnostics-template-record.cpp b/clang/test/Analysis/plist-diagnostics-template-record.cpp
--- a/clang/test/Analysis/plist-diagnostics-template-record.cpp
+++ b/clang/test/Analysis/plist-diagnostics-template-record.cpp
@@ -38,5 +38,5 @@
 
 // CHECK:      <string>Calling constructor for &apos;DivByZero&lt;int, float, double, 0&gt;&apos;</string>
 // CHECK:      <string>Calling constructor for &apos;DivByZero&lt;char, float, double, 0&gt;&apos;</string>
-// CHECK:      <string>Calling constructor for &apos;DivByZeroVariadic&lt;char, float, double, nullptr_t&gt;&apos;</string>
+// CHECK:      <string>Calling constructor for &apos;DivByZeroVariadic&lt;char, float, double, std::nullptr_t&gt;&apos;</string>
 
diff --git a/clang/test/CXX/drs/dr15xx.cpp b/clang/test/CXX/drs/dr15xx.cpp
--- a/clang/test/CXX/drs/dr15xx.cpp
+++ b/clang/test/CXX/drs/dr15xx.cpp
@@ -113,7 +113,7 @@
   }
 
 #if __cplusplus >= 201103L
-  template<typename T> struct Wrap { operator T(); }; // expected-note 4{{converted to type 'nullptr_t'}} expected-note 4{{converted to type 'int *'}}
+  template<typename T> struct Wrap { operator T(); }; // expected-note 4{{converted to type 'std::nullptr_t'}} expected-note 4{{converted to type 'int *'}}
   void test_overload() {
     using nullptr_t = decltype(nullptr);
     void(Wrap<nullptr_t>() == Wrap<nullptr_t>());
@@ -127,7 +127,7 @@
     // but then only convert as far as 'nullptr_t', which we then can't convert to 'int*'.
     void(Wrap<nullptr_t>() == Wrap<int*>());
     void(Wrap<nullptr_t>() != Wrap<int*>());
-    void(Wrap<nullptr_t>() < Wrap<int*>()); // expected-error {{invalid operands to binary expression ('Wrap<nullptr_t>' and 'Wrap<int *>')}}
+    void(Wrap<nullptr_t>() < Wrap<int*>()); // expected-error {{invalid operands to binary expression ('Wrap<nullptr_t>' (aka 'Wrap<std::nullptr_t>') and 'Wrap<int *>')}}
     void(Wrap<nullptr_t>() > Wrap<int*>()); // expected-error {{invalid operands}}
     void(Wrap<nullptr_t>() <= Wrap<int*>()); // expected-error {{invalid operands}}
     void(Wrap<nullptr_t>() >= Wrap<int*>()); // expected-error {{invalid operands}}
diff --git a/clang/test/CXX/drs/dr6xx.cpp b/clang/test/CXX/drs/dr6xx.cpp
--- a/clang/test/CXX/drs/dr6xx.cpp
+++ b/clang/test/CXX/drs/dr6xx.cpp
@@ -590,7 +590,7 @@
 namespace dr654 { // dr654: sup 1423
   void f() {
     if (nullptr) {} // expected-warning {{implicit conversion of nullptr constant to 'bool'}}
-    bool b = nullptr; // expected-error {{cannot initialize a variable of type 'bool' with an rvalue of type 'nullptr_t'}}
+    bool b = nullptr; // expected-error {{cannot initialize a variable of type 'bool' with an rvalue of type 'std::nullptr_t'}}
     if (nullptr == 0) {}
     if (nullptr != 0) {}
     if (nullptr <= 0) {} // expected-error {{invalid operands}}
diff --git a/clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp b/clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp
--- a/clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp
+++ b/clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp
@@ -24,7 +24,7 @@
 IP<get_nullptr()> ip3;
 IP<(int*)0> ip4;
 IP<np> ip5;
-IP<nonconst_np> ip5; // expected-error{{non-type template argument of type 'std::nullptr_t' (aka 'nullptr_t') is not a constant expression}} \
+IP<nonconst_np> ip5; // expected-error{{non-type template argument of type 'std::nullptr_t' is not a constant expression}} \
 // expected-note{{read of non-constexpr variable 'nonconst_np' is not allowed in a constant expression}}
 IP<(float*)0> ip6; // expected-error{{null non-type template argument of type 'float *' does not match template parameter of type 'int *'}}
 IP<&tl> ip7; // expected-error{{non-type template argument of type 'int *' is not a constant expression}}
@@ -62,6 +62,6 @@
 NP<nullptr> np1;
 NP<np> np2;
 NP<get_nullptr()> np3;
-NP<0> np4; // expected-error{{null non-type template argument must be cast to template parameter type 'std::nullptr_t' (aka 'nullptr_t')}}
+NP<0> np4; // expected-error{{null non-type template argument must be cast to template parameter type 'std::nullptr_t'}}
 constexpr int i = 7;
 NP<i> np5; // expected-error{{non-type template argument of type 'const int' cannot be converted to a value of type 'std::nullptr_t'}}
diff --git a/clang/test/CXX/temp/temp.param/p10-2a.cpp b/clang/test/CXX/temp/temp.param/p10-2a.cpp
--- a/clang/test/CXX/temp/temp.param/p10-2a.cpp
+++ b/clang/test/CXX/temp/temp.param/p10-2a.cpp
@@ -94,8 +94,8 @@
 // expected-note@-5 {{and 'is_same_v<short, char>' evaluated to false}}
 // expected-note@-6 3{{because 'is_same_v<int, char [1]>' evaluated to false}}
 // expected-note@-7 3{{and 'is_same_v<int, char [2]>' evaluated to false}}
-// expected-note@-8 2{{because 'is_same_v<nullptr_t, char>' evaluated to false}}
-// expected-note@-9 2{{and 'is_same_v<nullptr_t, int>' evaluated to false}}
+// expected-note@-8 2{{because 'is_same_v<std::nullptr_t, char>' evaluated to false}}
+// expected-note@-9 2{{and 'is_same_v<std::nullptr_t, int>' evaluated to false}}
 
 template<OneOf<char[1], char[2]> T, OneOf<int, long, char> U>
 // expected-note@-1 2{{because 'OneOf<char, char [1], char [2]>' evaluated to false}}
diff --git a/clang/test/OpenMP/task_affinity_messages.cpp b/clang/test/OpenMP/task_affinity_messages.cpp
--- a/clang/test/OpenMP/task_affinity_messages.cpp
+++ b/clang/test/OpenMP/task_affinity_messages.cpp
@@ -65,7 +65,7 @@
   #pragma omp task affinity(iterator(unsigned argc: // expected-error {{expected ')'}} expected-note {{to match this '('}} expected-error {{expected '=' in iterator specifier}} expected-error 2 {{expected expression}} expected-error {{expected ',' or ')' after iterator specifier}} expected-error {{expected ')'}} expected-note {{to match this '('}} expected-error {{expected expression}}
   #pragma omp task affinity(iterator(unsigned argc = // expected-error {{expected ')'}} expected-note {{to match this '('}} expected-error 2 {{expected expression}} expected-error {{expected ',' or ')' after iterator specifier}} expected-error {{expected ')'}} expected-note {{to match this '('}} expected-error {{expected expression}}
   #pragma omp task affinity(iterator(vector argc = 0:2):argc) // expected-error {{expected integral or pointer type as the iterator-type, not 'vector'}} expected-error {{expected expression}}
-  #pragma omp task affinity(iterator(vector *argc = nullptr:nullptr+2:0):argc) // expected-error {{invalid operands to binary expression ('nullptr_t' and 'int')}} expected-error {{iterator step expression 0 evaluates to 0}} expected-error {{expected expression}}
+  #pragma omp task affinity(iterator(vector *argc = nullptr:nullptr+2:0):argc) // expected-error {{invalid operands to binary expression ('std::nullptr_t' and 'int')}} expected-error {{iterator step expression 0 evaluates to 0}} expected-error {{expected expression}}
   #pragma omp task affinity(iterator(vector *argc = 0:vector():argc):argc) // expected-error {{converting 'vector' to incompatible type 'vector *'}} expected-error {{expected expression}}
   foo();
 #pragma omp task affinity(iterator(i = 0:10, i = 0:10) : argv[i]) // expected-error {{redefinition of 'i'}} expected-note {{previous definition is here}}
diff --git a/clang/test/OpenMP/task_depend_messages.cpp b/clang/test/OpenMP/task_depend_messages.cpp
--- a/clang/test/OpenMP/task_depend_messages.cpp
+++ b/clang/test/OpenMP/task_depend_messages.cpp
@@ -76,7 +76,7 @@
   #pragma omp task depend(iterator(unsigned argc: // expected-error {{expected ')'}} omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}} expected-warning {{missing ':' after dependency type - ignoring}} expected-note {{to match this '('}} omp50-error {{expected '=' in iterator specifier}} omp50-error 2 {{expected expression}} omp50-error {{expected ',' or ')' after iterator specifier}} omp50-error {{expected ')'}} omp50-error {{expected depend modifier(iterator) or 'in', 'out', 'inout', 'mutexinoutset' or 'depobj' in OpenMP clause 'depend'}} omp50-error {{expected ','}} omp50-note {{to match this '('}}
   #pragma omp task depend(iterator(unsigned argc = // expected-error {{expected ')'}} omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}} expected-warning {{missing ':' after dependency type - ignoring}} expected-note {{to match this '('}} omp50-error 2 {{expected expression}} omp50-error {{expected ',' or ')' after iterator specifier}} omp50-error {{expected ')'}} omp50-error {{expected depend modifier(iterator) or 'in', 'out', 'inout', 'mutexinoutset' or 'depobj' in OpenMP clause 'depend'}} omp50-error {{expected ','}} omp50-note {{to match this '('}}
   #pragma omp task depend(iterator(vector argc = 0:2):argc) // omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}} omp50-error {{expected integral or pointer type as the iterator-type, not 'vector'}} omp50-error {{expected depend modifier(iterator) or 'in', 'out', 'inout', 'mutexinoutset' or 'depobj' in OpenMP clause 'depend'}} omp50-error {{expected ','}}
-  #pragma omp task depend(iterator(vector *argc = nullptr:nullptr+2:0), in:argc) // omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}} omp50-error {{invalid operands to binary expression ('nullptr_t' and 'int')}} omp50-error {{iterator step expression 0 evaluates to 0}}
+  #pragma omp task depend(iterator(vector *argc = nullptr:nullptr+2:0), in:argc) // omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}} omp50-error {{invalid operands to binary expression ('std::nullptr_t' and 'int')}} omp50-error {{iterator step expression 0 evaluates to 0}}
   #pragma omp task depend(iterator(vector *argc = 0:vector():argc), in:argc) // omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}} omp50-error {{converting 'vector' to incompatible type 'vector *'}}
   foo();
 #pragma omp task depend(iterator(unsigned argc = 0:10), in : argc) // omp45-error {{expected 'in', 'out', 'inout' or 'mutexinoutset' in OpenMP clause 'depend'}}
diff --git a/clang/test/Sema/builtins-arm64-mte.c b/clang/test/Sema/builtins-arm64-mte.c
--- a/clang/test/Sema/builtins-arm64-mte.c
+++ b/clang/test/Sema/builtins-arm64-mte.c
@@ -130,7 +130,7 @@
 
 #ifdef __cplusplus
 ptrdiff_t subtract_pointers5() {
-  // expected-error@+1 {{at least one argument of MTE builtin function must be a pointer ('nullptr_t', 'nullptr_t' invalid)}}
+  // expected-error@+1 {{at least one argument of MTE builtin function must be a pointer ('std::nullptr_t', 'std::nullptr_t' invalid)}}
   return __arm_mte_ptrdiff(nullptr, nullptr);
 }
 #endif
diff --git a/clang/test/Sema/format-strings-pedantic.c b/clang/test/Sema/format-strings-pedantic.c
--- a/clang/test/Sema/format-strings-pedantic.c
+++ b/clang/test/Sema/format-strings-pedantic.c
@@ -15,6 +15,6 @@
 #endif
 
 #ifdef __cplusplus
-  printf("%p", nullptr); // expected-warning {{format specifies type 'void *' but the argument has type 'nullptr_t'}}
+  printf("%p", nullptr); // expected-warning {{format specifies type 'void *' but the argument has type 'std::nullptr_t'}}
 #endif
 }
diff --git a/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp b/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
--- a/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
+++ b/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
@@ -86,7 +86,7 @@
 void f() noexcept(sizeof(char[2])); // expected-error {{noexcept specifier argument evaluates to 2, which cannot be narrowed to type 'bool'}}
 void g() noexcept(sizeof(char));
 void h() noexcept(ptr);     // expected-error {{conversion from 'const int *' to 'bool' is not allowed in a converted constant expression}}
-void i() noexcept(nullptr); // expected-error {{conversion from 'nullptr_t' to 'bool' is not allowed in a converted constant expression}}
+void i() noexcept(nullptr); // expected-error {{conversion from 'std::nullptr_t' to 'bool' is not allowed in a converted constant expression}}
 void j() noexcept(0);
 void k() noexcept(1);
 void l() noexcept(2); // expected-error {{noexcept specifier argument evaluates to 2, which cannot be narrowed to type 'bool'}}
diff --git a/clang/test/SemaCXX/cxx2a-explicit-bool.cpp b/clang/test/SemaCXX/cxx2a-explicit-bool.cpp
--- a/clang/test/SemaCXX/cxx2a-explicit-bool.cpp
+++ b/clang/test/SemaCXX/cxx2a-explicit-bool.cpp
@@ -735,7 +735,7 @@
 struct S {
   explicit(sizeof(char[2])) S(char); // expected-error {{explicit specifier argument evaluates to 2, which cannot be narrowed to type 'bool'}}
   explicit(ptr) S(long);             // expected-error {{conversion from 'const int *' to 'bool' is not allowed in a converted constant expression}}
-  explicit(nullptr) S(int);          // expected-error {{conversion from 'nullptr_t' to 'bool' is not allowed in a converted constant expression}}
+  explicit(nullptr) S(int);          // expected-error {{conversion from 'std::nullptr_t' to 'bool' is not allowed in a converted constant expression}}
   explicit(42L) S(int, int);         // expected-error {{explicit specifier argument evaluates to 42, which cannot be narrowed to type 'bool'}}
   explicit(sizeof(char)) S();
   explicit(0) S(char, char);
diff --git a/clang/test/SemaCXX/nullability.cpp b/clang/test/SemaCXX/nullability.cpp
--- a/clang/test/SemaCXX/nullability.cpp
+++ b/clang/test/SemaCXX/nullability.cpp
@@ -15,7 +15,7 @@
 // Nullability applies to all pointer types.
 typedef int (X::* _Nonnull member_function_type_1)(int);
 typedef int X::* _Nonnull member_data_type_1;
-typedef nullptr_t _Nonnull nonnull_nullptr_t; // expected-error{{nullability specifier '_Nonnull' cannot be applied to non-pointer type 'nullptr_t'}}
+typedef nullptr_t _Nonnull nonnull_nullptr_t; // expected-error{{nullability specifier '_Nonnull' cannot be applied to non-pointer type 'nullptr_t' (aka 'std::nullptr_t')}}
 
 // Nullability can move into member pointers (this is suppressing a warning).
 typedef _Nonnull int (X::* member_function_type_2)(int);
@@ -26,7 +26,7 @@
 template<typename T>
 struct AddNonNull {
   typedef _Nonnull T type; // expected-error{{nullability specifier '_Nonnull' cannot be applied to non-pointer type 'int'}}
-  // expected-error@-1{{nullability specifier '_Nonnull' cannot be applied to non-pointer type 'nullptr_t'}}
+  // expected-error@-1{{nullability specifier '_Nonnull' cannot be applied to non-pointer type 'std::nullptr_t'}}
 };
 
 typedef AddNonNull<int *>::type nonnull_int_ptr_1;
diff --git a/clang/test/SemaCXX/nullptr.cpp b/clang/test/SemaCXX/nullptr.cpp
--- a/clang/test/SemaCXX/nullptr.cpp
+++ b/clang/test/SemaCXX/nullptr.cpp
@@ -57,7 +57,7 @@
   o2(nullptr); // expected-error {{ambiguous}}
 
   // nullptr is an rvalue, null is an lvalue
-  (void)&nullptr; // expected-error {{cannot take the address of an rvalue of type 'nullptr_t'}}
+  (void)&nullptr; // expected-error {{cannot take the address of an rvalue of type 'std::nullptr_t'}}
   nullptr_t *pn = &null;
 
   // You can reinterpret_cast nullptr to an integer.
diff --git a/clang/test/SemaTemplate/deduction-guide.cpp b/clang/test/SemaTemplate/deduction-guide.cpp
--- a/clang/test/SemaTemplate/deduction-guide.cpp
+++ b/clang/test/SemaTemplate/deduction-guide.cpp
@@ -73,7 +73,7 @@
 // CHECK: `-CXXDeductionGuideDecl {{.*}} 'auto (X<nullptr, 'x'>) -> B<char, 'x'>'
 // CHECK:   |-TemplateArgument type 'char'
 // CHECK:   |-TemplateArgument integral 120
-// CHECK:   |-TemplateArgument type 'nullptr_t'
+// CHECK:   |-TemplateArgument type 'std::nullptr_t'
 // CHECK:   |-TemplateArgument nullptr
 // CHECK:   `-ParmVarDecl {{.*}} 'X<nullptr, 'x'>':'X<nullptr, 'x'>'
 // CHECK: FunctionProtoType {{.*}} 'auto (X<W, V>) -> B<T, V>' dependent trailing_return
diff --git a/clang/test/SemaTemplate/deduction.cpp b/clang/test/SemaTemplate/deduction.cpp
--- a/clang/test/SemaTemplate/deduction.cpp
+++ b/clang/test/SemaTemplate/deduction.cpp
@@ -313,7 +313,7 @@
   }
 
   template<template<typename T, T> class X, typename T, int *P>
-    void f0(X<T, P>) {} // expected-note {{deduced non-type template argument does not have the same type as the corresponding template parameter ('nullptr_t' vs 'int *')}}
+    void f0(X<T, P>) {} // expected-note {{deduced non-type template argument does not have the same type as the corresponding template parameter ('std::nullptr_t' vs 'int *')}}
   void h0() {
     f0(X<int*, nullptr>());
     f0(X<nullptr_t, nullptr>()); // expected-error {{no matching function}}
diff --git a/clang/test/SemaTemplate/friend.cpp b/clang/test/SemaTemplate/friend.cpp
--- a/clang/test/SemaTemplate/friend.cpp
+++ b/clang/test/SemaTemplate/friend.cpp
@@ -146,5 +146,5 @@
   template<typename X> struct T { friend auto f(X*) { return nullptr; } };
   struct X1 { friend auto f(X1*); };
   template struct T<X1>;
-  int n = f((X1*)nullptr); // expected-error {{cannot initialize a variable of type 'int' with an rvalue of type 'nullptr_t'}}
+  int n = f((X1*)nullptr); // expected-error {{cannot initialize a variable of type 'int' with an rvalue of type 'std::nullptr_t'}}
 }
diff --git a/clang/test/SemaTemplate/instantiate-local-class.cpp b/clang/test/SemaTemplate/instantiate-local-class.cpp
--- a/clang/test/SemaTemplate/instantiate-local-class.cpp
+++ b/clang/test/SemaTemplate/instantiate-local-class.cpp
@@ -489,7 +489,7 @@
 namespace PR45000 {
   template <typename T>
   void f(int x = [](T x = nullptr) -> int { return x; }());
-  // expected-error@-1 {{cannot initialize a parameter of type 'int' with an rvalue of type 'nullptr_t'}}
+  // expected-error@-1 {{cannot initialize a parameter of type 'int' with an rvalue of type 'std::nullptr_t'}}
   // expected-note@-2 {{passing argument to parameter 'x' here}}
 
   void g() { f<int>(); }