diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 16639f0..5ad673a 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -3893,6 +3893,13 @@
 
   handleDeclspecAlignBeforeClassKey(attrs, DS, TUK);
 
+  Sema::SkipBodyInfo SkipBody;
+  if (!Name && TUK == Sema::TUK_Definition && Tok.is(tok::l_brace) &&
+      NextToken().is(tok::identifier))
+    SkipBody = Actions.shouldSkipAnonEnumBody(getCurScope(),
+                                              NextToken().getIdentifierInfo(),
+                                              NextToken().getLocation());
+
   bool Owned = false;
   bool IsDependent = false;
   const char *PrevSpec = nullptr;
@@ -3902,7 +3909,22 @@
                                    AS, DS.getModulePrivateSpecLoc(), TParams,
                                    Owned, IsDependent, ScopedEnumKWLoc,
                                    IsScopedUsingClassTag, BaseType,
-                                   DSC == DSC_type_specifier);
+                                   DSC == DSC_type_specifier, &SkipBody);
+
+  if (SkipBody.ShouldSkip) {
+    assert(TUK == Sema::TUK_Definition && "can only skip a definition");
+
+    BalancedDelimiterTracker T(*this, tok::l_brace);
+    T.consumeOpen();
+    T.skipToEnd();
+
+    if (DS.SetTypeSpecType(DeclSpec::TST_enum, StartLoc,
+                           NameLoc.isValid() ? NameLoc : StartLoc,
+                           PrevSpec, DiagID, TagDecl, Owned,
+                           Actions.getASTContext().getPrintingPolicy()))
+      Diag(StartLoc, DiagID) << PrevSpec;
+    return;
+  }
 
   if (IsDependent) {
     // This enum has a dependent nested-name-specifier. Handle it as a
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 11934c4..bb7ae63 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -1553,7 +1553,7 @@
   TypeResult TypeResult = true; // invalid
 
   bool Owned = false;
-  bool SkipBody = false;
+  Sema::SkipBodyInfo SkipBody;
   if (TemplateId) {
     // Explicit specialization, class template partial specialization,
     // or explicit instantiation.
@@ -1718,7 +1718,7 @@
     assert(Tok.is(tok::l_brace) ||
            (getLangOpts().CPlusPlus && Tok.is(tok::colon)) ||
            isCXX11FinalKeyword());
-    if (SkipBody)
+    if (SkipBody.ShouldSkip)
       SkipCXXMemberSpecification(StartLoc, AttrFixitLoc, TagType,
                                  TagOrTempResult.get());
     else if (getLangOpts().CPlusPlus)
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 7f4b395..bc31d46 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16,7 +16,6 @@
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTLambda.h"
-#include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/CommentDiagnostic.h"
@@ -1974,9 +1973,7 @@
         New->setTypeSourceInfo(OldTD->getTypeSourceInfo());
 
       // Make the old tag definition visible.
-      if (auto *Listener = getASTMutationListener())
-        Listener->RedefinedHiddenDefinition(Hidden, NewTag->getLocation());
-      Hidden->setHidden(false);
+      makeMergedDefinitionVisible(Hidden, NewTag->getLocation());
     }
   }
 
@@ -11311,8 +11308,8 @@
 /// \param IsTypeSpecifier \c true if this is a type-specifier (or
 /// trailing-type-specifier) other than one in an alias-declaration.
 ///
-/// \param SkipBody If non-null, will be set to true if the caller should skip
-/// the definition of this tag, and treat it as if it were a declaration.
+/// \param SkipBody If non-null, will be set to indicate if the caller should
+/// skip the definition of this tag and treat it as if it were a declaration.
 Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                      SourceLocation KWLoc, CXXScopeSpec &SS,
                      IdentifierInfo *Name, SourceLocation NameLoc,
@@ -11323,7 +11320,7 @@
                      SourceLocation ScopedEnumKWLoc,
                      bool ScopedEnumUsesClassTag,
                      TypeResult UnderlyingType,
-                     bool IsTypeSpecifier, bool *SkipBody) {
+                     bool IsTypeSpecifier, SkipBodyInfo *SkipBody) {
   // If this is not a definition, it must have a name.
   IdentifierInfo *OrigName = Name;
   assert((Name != nullptr || TUK == TUK_Definition) &&
@@ -11633,6 +11630,10 @@
     }
   }
 
+  // If we have a known previous declaration to use, then use it.
+  if (Previous.empty() && SkipBody && SkipBody->Previous)
+    Previous.addDecl(SkipBody->Previous);
+
   if (!Previous.empty()) {
     NamedDecl *PrevDecl = Previous.getFoundDecl();
     NamedDecl *DirectPrevDecl =
@@ -11774,10 +11775,8 @@
                 // assume that this definition is identical to the hidden one
                 // we already have. Make the existing definition visible and
                 // use it in place of this one.
-                *SkipBody = true;
-                if (auto *Listener = getASTMutationListener())
-                  Listener->RedefinedHiddenDefinition(Hidden, KWLoc);
-                Hidden->setHidden(false);
+                SkipBody->ShouldSkip = true;
+                makeMergedDefinitionVisible(Hidden, KWLoc);
                 return Def;
               } else if (!IsExplicitSpecializationAfterInstantiation) {
                 // A redeclaration in function prototype scope in C isn't
@@ -13465,6 +13464,29 @@
                                   Val, EnumVal);
 }
 
+Sema::SkipBodyInfo Sema::shouldSkipAnonEnumBody(Scope *S, IdentifierInfo *II,
+                                                SourceLocation IILoc) {
+  if (!getLangOpts().Modules || !getLangOpts().CPlusPlus)
+    return SkipBodyInfo();
+
+  // We have an anonymous enum definition. Look up the first enumerator to
+  // determine if we should merge the definition with an existing one and
+  // skip the body.
+  NamedDecl *PrevDecl = LookupSingleName(S, II, IILoc, LookupOrdinaryName,
+                                         ForRedeclaration);
+  auto *PrevECD = dyn_cast_or_null<EnumConstantDecl>(PrevDecl);
+  NamedDecl *Hidden;
+  if (PrevECD &&
+      !hasVisibleDefinition(cast<NamedDecl>(PrevECD->getDeclContext()),
+                            &Hidden)) {
+    SkipBodyInfo Skip;
+    Skip.ShouldSkip = true;
+    Skip.Previous = Hidden;
+    return Skip;
+  }
+
+  return SkipBodyInfo();
+}
 
 Decl *Sema::ActOnEnumConstant(Scope *S, Decl *theEnumDecl, Decl *lastEnumConst,
                               SourceLocation IdLoc, IdentifierInfo *Id,
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 09424a4..012c1cf 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 #include "clang/Sema/Lookup.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
@@ -1169,6 +1170,12 @@
   return MSInfo->isExplicitSpecialization() ? D : MSInfo->getInstantiatedFrom();
 }
 
+void Sema::makeMergedDefinitionVisible(NamedDecl *ND, SourceLocation Loc) {
+  if (auto *Listener = getASTMutationListener())
+    Listener->RedefinedHiddenDefinition(ND, Loc);
+  ND->setHidden(false);
+}
+
 /// \brief Find the module in which the given declaration was defined.
 static Module *getDefiningModule(Decl *Entity) {
   if (FunctionDecl *FD = dyn_cast<FunctionDecl>(Entity)) {
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index c642c05..687e611 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -12,7 +12,6 @@
 #include "TreeTransform.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
-#include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/DeclFriend.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
@@ -838,7 +837,7 @@
                          SourceLocation FriendLoc,
                          unsigned NumOuterTemplateParamLists,
                          TemplateParameterList** OuterTemplateParamLists,
-                         bool *SkipBody) {
+                         SkipBodyInfo *SkipBody) {
   assert(TemplateParams && TemplateParams->size() > 0 &&
          "No template parameters");
   assert(TUK != TUK_Reference && "Can only declare or define class templates");
@@ -999,16 +998,12 @@
         // simply making that previous definition visible.
         NamedDecl *Hidden = nullptr;
         if (SkipBody && !hasVisibleDefinition(Def, &Hidden)) {
-          *SkipBody = true;
+          SkipBody->ShouldSkip = true;
           auto *Tmpl = cast<CXXRecordDecl>(Hidden)->getDescribedClassTemplate();
           assert(Tmpl && "original definition of a class template is not a "
                          "class template?");
-          if (auto *Listener = getASTMutationListener()) {
-            Listener->RedefinedHiddenDefinition(Hidden, KWLoc);
-            Listener->RedefinedHiddenDefinition(Tmpl, KWLoc);
-          }
-          Hidden->setHidden(false);
-          Tmpl->setHidden(false);
+          makeMergedDefinitionVisible(Hidden, KWLoc);
+          makeMergedDefinitionVisible(Tmpl, KWLoc);
           return Def;
         }