diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e671183522565..555fa1955ba45 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -421,6 +421,11 @@ Bug Fixes to C++ Support
 - Clang now issues an error when placement new is used to modify a const-qualified variable
   in a ``constexpr`` function. (#GH131432)
 - Clang now emits a warning when class template argument deduction for alias templates is used in C++17. (#GH133806)
+- No longer add enumerators to the scope chain when the enumeration is declared
+  within a class context but is defined out of line. Previously, the
+  enumerators were being added both to the class context and to the namespace
+  scope. (#GH23317)
+
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index 798f112ce7200..4a510def90057 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -3347,6 +3347,8 @@ class EnumConstantDecl : public ValueDecl,
   EnumConstantDecl *getCanonicalDecl() override { return getFirstDecl(); }
   const EnumConstantDecl *getCanonicalDecl() const { return getFirstDecl(); }
 
+  bool isOutOfLine() const override;
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == EnumConstant; }
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 83116ecc0f47b..9d10b02ea1f75 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -5585,6 +5585,18 @@ SourceRange EnumConstantDecl::getSourceRange() const {
   return SourceRange(getLocation(), End);
 }
 
+bool EnumConstantDecl::isOutOfLine() const {
+  if (Decl::isOutOfLine())
+    return true;
+
+  // In C++, if the enumeration is out of line, the enumeration constants are
+  // also out of line.
+  if (getLangOpts().CPlusPlus)
+    return cast<Decl>(getDeclContext())->isOutOfLine();
+
+  return false;
+}
+
 void TypeDecl::anchor() {}
 
 TypedefDecl *TypedefDecl::Create(ASTContext &C, DeclContext *DC,
diff --git a/clang/test/CXX/temp/temp.decls/temp.class/temp.mem.enum/p1.cpp b/clang/test/CXX/temp/temp.decls/temp.class/temp.mem.enum/p1.cpp
index e5807993a7a18..f41f3f39f2784 100644
--- a/clang/test/CXX/temp/temp.decls/temp.class/temp.mem.enum/p1.cpp
+++ b/clang/test/CXX/temp/temp.decls/temp.class/temp.mem.enum/p1.cpp
@@ -12,7 +12,7 @@ A<int> a;
 A<int>::E a0 = A<int>().v;
 int n = A<int>::E::e1; // expected-error {{implicit instantiation of undefined member}}
 
-template<typename T> enum A<T>::E : T { e1, e2 }; // expected-note 2 {{declared here}}
+template<typename T> enum A<T>::E : T { e1, e2 };
 
 // FIXME: Now that A<T>::E is defined, we are supposed to inject its enumerators
 // into the already-instantiated class A<T>. This seems like a really bad idea,
@@ -20,7 +20,7 @@ template<typename T> enum A<T>::E : T { e1, e2 }; // expected-note 2 {{declared
 //
 // Either do as the standard says, or only include enumerators lexically defined
 // within the class in its scope.
-A<int>::E a1 = A<int>::e1; // expected-error {{no member named 'e1' in 'A<int>'; did you mean simply 'e1'?}}
+A<int>::E a1 = A<int>::e1; // expected-error {{no member named 'e1' in 'A<int>'}}
 
 A<char>::E a2 = A<char>::e2;
 
@@ -43,7 +43,7 @@ B<int>::E b1 = B<int>::E::e1;
 
 B<char>::E b2 = B<char>::E::e2;
 
-template<typename T> typename B<T>::E B<T>::g() { return e2; }
+template<typename T> typename B<T>::E B<T>::g() { return e2; } // expected-error {{use of undeclared identifier 'e2'}}
 B<short>::E b3 = B<short>().g();
 
 
@@ -94,7 +94,7 @@ D<int>::E d1 = D<int>::E::e1; // expected-error {{incomplete type 'D<int>::E'}}
 template<> enum class D<int>::E { e2 };
 D<int>::E d2 = D<int>::E::e2;
 D<char>::E d3 = D<char>::E::e1; // expected-note {{first required here}}
-D<char>::E d4 = D<char>::E::e2; // expected-error {{no member named 'e2' in 'D<char>::E'; did you mean simply 'e2'?}}
+D<char>::E d4 = D<char>::E::e2; // expected-error {{no member named 'e2' in 'D<char>::E'}}
 template<> enum class D<char>::E { e3 }; // expected-error {{explicit specialization of 'E' after instantiation}}
 
 template<> enum class D<short>::E;
diff --git a/clang/test/SemaCXX/enum.cpp b/clang/test/SemaCXX/enum.cpp
index 44042d8bf5cfc..e2cda23269d76 100644
--- a/clang/test/SemaCXX/enum.cpp
+++ b/clang/test/SemaCXX/enum.cpp
@@ -151,3 +151,21 @@ class C {
                         // expected-error {{unexpected ';' before ')'}}
 };
 }
+
+#if __cplusplus >= 201103L
+namespace GH23317 {
+struct A {
+  enum E : int;
+  constexpr int foo() const;
+};
+
+enum A::E : int  { ae1 = 100, ae2 }; // expected-note {{'A::ae1' declared here}}
+
+constexpr int A::foo() const { return ae1; } // This is fine
+static_assert(A{}.foo() == 100, "oh no");
+
+int foo() {
+  return ae1; // expected-error {{use of undeclared identifier 'ae1'; did you mean 'A::ae1'?}}
+}
+} // namespace GH23317
+#endif // __cplusplus >= 201103L