diff --git a/flang/examples/FeatureList/FeatureList.cpp b/flang/examples/FeatureList/FeatureList.cpp
index e35f120d8661e..ddb9dee5b8a8e 100644
--- a/flang/examples/FeatureList/FeatureList.cpp
+++ b/flang/examples/FeatureList/FeatureList.cpp
@@ -514,7 +514,7 @@ struct NodeVisitor {
   READ_FEATURE(OmpReductionClause)
   READ_FEATURE(OmpInReductionClause)
   READ_FEATURE(OmpReductionCombiner)
-  READ_FEATURE(OmpReductionInitializerClause)
+  READ_FEATURE(OmpInitializerClause)
   READ_FEATURE(OmpReductionIdentifier)
   READ_FEATURE(OmpAllocateClause)
   READ_FEATURE(OmpAllocateClause::Modifier)
diff --git a/flang/include/flang/Parser/dump-parse-tree.h b/flang/include/flang/Parser/dump-parse-tree.h
index 5400d6fac98a9..3b3c6bdc448d7 100644
--- a/flang/include/flang/Parser/dump-parse-tree.h
+++ b/flang/include/flang/Parser/dump-parse-tree.h
@@ -638,9 +638,9 @@ class ParseTreeDumper {
   NODE(parser, OmpReductionCombiner)
   NODE(parser, OmpTaskReductionClause)
   NODE(OmpTaskReductionClause, Modifier)
-  NODE(parser, OmpReductionInitializerProc)
-  NODE(parser, OmpReductionInitializerExpr)
-  NODE(parser, OmpReductionInitializerClause)
+  NODE(parser, OmpInitializerProc)
+  NODE(parser, OmpInitializerExpr)
+  NODE(parser, OmpInitializerClause)
   NODE(parser, OmpReductionIdentifier)
   NODE(parser, OmpAllocateClause)
   NODE(OmpAllocateClause, Modifier)
diff --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
index 2d56a6c9469db..f11859bb09ddb 100644
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -4246,6 +4246,20 @@ struct OmpInReductionClause {
   std::tuple<MODIFIERS(), OmpObjectList> t;
 };
 
+// declare-reduction -> DECLARE REDUCTION (reduction-identifier : type-list
+//                                              : combiner) [initializer-clause]
+struct OmpInitializerProc {
+  TUPLE_CLASS_BOILERPLATE(OmpInitializerProc);
+  std::tuple<ProcedureDesignator, std::list<ActualArgSpec>> t;
+};
+WRAPPER_CLASS(OmpInitializerExpr, Expr);
+
+// Initialization for declare reduction construct
+struct OmpInitializerClause {
+  UNION_CLASS_BOILERPLATE(OmpInitializerClause);
+  std::variant<OmpInitializerProc, OmpInitializerExpr> u;
+};
+
 // Ref: [4.5:199-201], [5.0:288-290], [5.1:321-322], [5.2:115-117]
 //
 // lastprivate-clause ->
@@ -4627,24 +4641,14 @@ struct OpenMPDeclareMapperConstruct {
   std::tuple<Verbatim, OmpMapperSpecifier, OmpClauseList> t;
 };
 
+// ref: 5.2: Section 5.5.11 139-141
 // 2.16 declare-reduction -> DECLARE REDUCTION (reduction-identifier : type-list
 //                                              : combiner) [initializer-clause]
-struct OmpReductionInitializerProc {
-  TUPLE_CLASS_BOILERPLATE(OmpReductionInitializerProc);
-  std::tuple<ProcedureDesignator, std::list<ActualArgSpec>> t;
-};
-WRAPPER_CLASS(OmpReductionInitializerExpr, Expr);
-
-struct OmpReductionInitializerClause {
-  UNION_CLASS_BOILERPLATE(OmpReductionInitializerClause);
-  std::variant<OmpReductionInitializerProc, OmpReductionInitializerExpr> u;
-};
-
 struct OpenMPDeclareReductionConstruct {
   TUPLE_CLASS_BOILERPLATE(OpenMPDeclareReductionConstruct);
   CharBlock source;
   std::tuple<Verbatim, common::Indirection<OmpReductionSpecifier>,
-      std::optional<OmpReductionInitializerClause>>
+      std::optional<OmpClauseList>>
       t;
 };
 
diff --git a/flang/lib/Lower/OpenMP/Clauses.cpp b/flang/lib/Lower/OpenMP/Clauses.cpp
index 831ba23870360..84092b75e0b3c 100644
--- a/flang/lib/Lower/OpenMP/Clauses.cpp
+++ b/flang/lib/Lower/OpenMP/Clauses.cpp
@@ -863,7 +863,10 @@ Init make(const parser::OmpClause::Init &inp,
   llvm_unreachable("Empty: init");
 }
 
-// Initializer: missing-in-parser
+Initializer make(const parser::OmpClause::Initializer &inp,
+                 semantics::SemanticsContext &semaCtx) {
+  llvm_unreachable("Empty: initializer");
+}
 
 InReduction make(const parser::OmpClause::InReduction &inp,
                  semantics::SemanticsContext &semaCtx) {
diff --git a/flang/lib/Lower/OpenMP/Clauses.h b/flang/lib/Lower/OpenMP/Clauses.h
index 0f172e0acf626..23c984412df3e 100644
--- a/flang/lib/Lower/OpenMP/Clauses.h
+++ b/flang/lib/Lower/OpenMP/Clauses.h
@@ -231,6 +231,7 @@ using Inbranch = tomp::clause::InbranchT<TypeTy, IdTy, ExprTy>;
 using Inclusive = tomp::clause::InclusiveT<TypeTy, IdTy, ExprTy>;
 using Indirect = tomp::clause::IndirectT<TypeTy, IdTy, ExprTy>;
 using Init = tomp::clause::InitT<TypeTy, IdTy, ExprTy>;
+using Initializer = tomp::clause::InitializerT<TypeTy, IdTy, ExprTy>;
 using InReduction = tomp::clause::InReductionT<TypeTy, IdTy, ExprTy>;
 using IsDevicePtr = tomp::clause::IsDevicePtrT<TypeTy, IdTy, ExprTy>;
 using Lastprivate = tomp::clause::LastprivateT<TypeTy, IdTy, ExprTy>;
diff --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
index 6409d9c4908f2..43cd2ea1eb0e6 100644
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -855,6 +855,8 @@ TYPE_PARSER("ABSENT" >> construct<OmpClause>(construct<OmpClause::Absent>(
     "INBRANCH" >> construct<OmpClause>(construct<OmpClause::Inbranch>()) ||
     "INCLUSIVE" >> construct<OmpClause>(construct<OmpClause::Inclusive>(
                        parenthesized(Parser<OmpObjectList>{}))) ||
+    "INITIALIZER" >> construct<OmpClause>(construct<OmpClause::Initializer>(
+                         parenthesized(Parser<OmpInitializerClause>{}))) ||
     "IS_DEVICE_PTR" >> construct<OmpClause>(construct<OmpClause::IsDevicePtr>(
                            parenthesized(Parser<OmpObjectList>{}))) ||
     "LASTPRIVATE" >> construct<OmpClause>(construct<OmpClause::Lastprivate>(
@@ -1174,22 +1176,19 @@ TYPE_PARSER(construct<OmpBlockDirective>(first(
 TYPE_PARSER(sourced(construct<OmpBeginBlockDirective>(
     sourced(Parser<OmpBlockDirective>{}), Parser<OmpClauseList>{})))
 
-TYPE_PARSER(construct<OmpReductionInitializerExpr>("OMP_PRIV =" >> expr))
-TYPE_PARSER(
-    construct<OmpReductionInitializerProc>(Parser<ProcedureDesignator>{},
-        parenthesized(many(maybe(","_tok) >> Parser<ActualArgSpec>{}))))
+TYPE_PARSER(construct<OmpInitializerExpr>("OMP_PRIV =" >> expr))
+TYPE_PARSER(construct<OmpInitializerProc>(Parser<ProcedureDesignator>{},
+    parenthesized(many(maybe(","_tok) >> Parser<ActualArgSpec>{}))))
 
-TYPE_PARSER(construct<OmpReductionInitializerClause>(
-    "INITIALIZER" >> parenthesized(construct<OmpReductionInitializerClause>(
-                                       Parser<OmpReductionInitializerExpr>{}) ||
-                         construct<OmpReductionInitializerClause>(
-                             Parser<OmpReductionInitializerProc>{}))))
+TYPE_PARSER(construct<OmpInitializerClause>(
+    construct<OmpInitializerClause>(Parser<OmpInitializerExpr>{}) ||
+    construct<OmpInitializerClause>(Parser<OmpInitializerProc>{})))
 
 // 2.16 Declare Reduction Construct
 TYPE_PARSER(sourced(construct<OpenMPDeclareReductionConstruct>(
     verbatim("DECLARE REDUCTION"_tok),
     "(" >> indirect(Parser<OmpReductionSpecifier>{}) / ")",
-    maybe(Parser<OmpReductionInitializerClause>{}))))
+    maybe(Parser<OmpClauseList>{}))))
 
 // declare-target with list
 TYPE_PARSER(sourced(construct<OmpDeclareTargetWithList>(
diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
index e55cc97429b49..1df17b6d7382b 100644
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -2699,28 +2699,24 @@ class UnparseVisitor {
   void Unparse(const OmpDeclareTargetWithList &x) {
     Put("("), Walk(x.v), Put(")");
   }
-  void Unparse(const OmpReductionInitializerProc &x) {
+  void Unparse(const OmpInitializerProc &x) {
     Walk(std::get<ProcedureDesignator>(x.t));
     Put("(");
     Walk(std::get<std::list<ActualArgSpec>>(x.t));
     Put(")");
   }
-  void Unparse(const OmpReductionInitializerExpr &x) {
+  void Unparse(const OmpInitializerExpr &x) {
     Word("OMP_PRIV = ");
     Walk(x.v);
   }
-  void Unparse(const OmpReductionInitializerClause &x) {
-    Word(" INITIALIZER(");
-    Walk(x.u);
-    Put(")");
-  }
+  void Unparse(const OmpInitializerClause &x) { Walk(x.u); }
   void Unparse(const OpenMPDeclareReductionConstruct &x) {
     BeginOpenMP();
     Word("!$OMP DECLARE REDUCTION ");
     Put("(");
     Walk(std::get<common::Indirection<OmpReductionSpecifier>>(x.t));
     Put(")");
-    Walk(std::get<std::optional<OmpReductionInitializerClause>>(x.t));
+    Walk(std::get<std::optional<OmpClauseList>>(x.t));
     Put("\n");
     EndOpenMP();
   }
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 75602ca911429..c6ed211549401 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -1678,6 +1678,18 @@ void OmpStructureChecker::Leave(const parser::OpenMPDeclareMapperConstruct &) {
   dirContext_.pop_back();
 }
 
+void OmpStructureChecker::Enter(
+    const parser::OpenMPDeclareReductionConstruct &x) {
+  const auto &dir{std::get<parser::Verbatim>(x.t)};
+  PushContextAndClauseSets(
+      dir.source, llvm::omp::Directive::OMPD_declare_reduction);
+}
+
+void OmpStructureChecker::Leave(
+    const parser::OpenMPDeclareReductionConstruct &) {
+  dirContext_.pop_back();
+}
+
 void OmpStructureChecker::Enter(const parser::OpenMPDeclareTargetConstruct &x) {
   const auto &dir{std::get<parser::Verbatim>(x.t)};
   PushContext(dir.source, llvm::omp::Directive::OMPD_declare_target);
@@ -2990,6 +3002,7 @@ CHECK_SIMPLE_CLAUSE(Grainsize, OMPC_grainsize)
 CHECK_SIMPLE_CLAUSE(Hint, OMPC_hint)
 CHECK_SIMPLE_CLAUSE(Holds, OMPC_holds)
 CHECK_SIMPLE_CLAUSE(Inclusive, OMPC_inclusive)
+CHECK_SIMPLE_CLAUSE(Initializer, OMPC_initializer)
 CHECK_SIMPLE_CLAUSE(Match, OMPC_match)
 CHECK_SIMPLE_CLAUSE(Nontemporal, OMPC_nontemporal)
 CHECK_SIMPLE_CLAUSE(NumTasks, OMPC_num_tasks)
diff --git a/flang/lib/Semantics/check-omp-structure.h b/flang/lib/Semantics/check-omp-structure.h
index 63278616bbf5b..b70ea58cf5578 100644
--- a/flang/lib/Semantics/check-omp-structure.h
+++ b/flang/lib/Semantics/check-omp-structure.h
@@ -102,6 +102,8 @@ class OmpStructureChecker
   void Leave(const parser::OpenMPDeclarativeAllocate &);
   void Enter(const parser::OpenMPDeclareMapperConstruct &);
   void Leave(const parser::OpenMPDeclareMapperConstruct &);
+  void Enter(const parser::OpenMPDeclareReductionConstruct &);
+  void Leave(const parser::OpenMPDeclareReductionConstruct &);
   void Enter(const parser::OpenMPDeclareTargetConstruct &);
   void Leave(const parser::OpenMPDeclareTargetConstruct &);
   void Enter(const parser::OpenMPDepobjConstruct &);
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index c582b690a293d..848830e831427 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -1482,7 +1482,7 @@ class OmpVisitor : public virtual DeclarationVisitor {
     return false;
   }
 
-  bool Pre(const parser::OmpReductionInitializerProc &x) {
+  bool Pre(const parser::OmpInitializerProc &x) {
     auto &procDes = std::get<parser::ProcedureDesignator>(x.t);
     auto &name = std::get<parser::Name>(procDes.u);
     auto *symbol{FindSymbol(NonDerivedTypeScope(), name)};
@@ -1496,13 +1496,9 @@ class OmpVisitor : public virtual DeclarationVisitor {
 
   bool Pre(const parser::OpenMPDeclareReductionConstruct &x) {
     AddOmpSourceRange(x.source);
-    parser::OmpClauseList emptyList{std::list<parser::OmpClause>{}};
     ProcessReductionSpecifier(
         std::get<Indirection<parser::OmpReductionSpecifier>>(x.t).value(),
-        emptyList);
-    auto &init =
-        std::get<std::optional<parser::OmpReductionInitializerClause>>(x.t);
-    Walk(init);
+        std::get<std::optional<parser::OmpClauseList>>(x.t));
     return false;
   }
   bool Pre(const parser::OmpMapClause &);
@@ -1659,7 +1655,7 @@ class OmpVisitor : public virtual DeclarationVisitor {
   void ProcessMapperSpecifier(const parser::OmpMapperSpecifier &spec,
       const parser::OmpClauseList &clauses);
   void ProcessReductionSpecifier(const parser::OmpReductionSpecifier &spec,
-      const parser::OmpClauseList &clauses);
+      const std::optional<parser::OmpClauseList> &clauses);
 };
 
 bool OmpVisitor::NeedsScope(const parser::OpenMPBlockConstruct &x) {
@@ -1754,7 +1750,7 @@ void OmpVisitor::ProcessMapperSpecifier(const parser::OmpMapperSpecifier &spec,
 
 void OmpVisitor::ProcessReductionSpecifier(
     const parser::OmpReductionSpecifier &spec,
-    const parser::OmpClauseList &clauses) {
+    const std::optional<parser::OmpClauseList> &clauses) {
   const auto &id{std::get<parser::OmpReductionIdentifier>(spec.t)};
   if (auto procDes{std::get_if<parser::ProcedureDesignator>(&id.u)}) {
     if (auto *name{std::get_if<parser::Name>(&procDes->u)}) {
@@ -1796,7 +1792,7 @@ bool OmpVisitor::Pre(const parser::OmpDirectiveSpecification &x) {
     if (maybeArgs && maybeClauses) {
       const parser::OmpArgument &first{maybeArgs->front()};
       if (auto *spec{std::get_if<parser::OmpReductionSpecifier>(&first.u)}) {
-        ProcessReductionSpecifier(*spec, *maybeClauses);
+        ProcessReductionSpecifier(*spec, maybeClauses);
       }
     }
     break;
diff --git a/flang/test/Parser/OpenMP/declare-reduction-unparse.f90 b/flang/test/Parser/OpenMP/declare-reduction-unparse.f90
index e7b15fb3e9d2c..f0ab99f5cfb5f 100644
--- a/flang/test/Parser/OpenMP/declare-reduction-unparse.f90
+++ b/flang/test/Parser/OpenMP/declare-reduction-unparse.f90
@@ -23,7 +23,7 @@ end subroutine initme
 !$omp declare reduction(red_add:integer(4):omp_out=omp_out+omp_in) initializer(initme(omp_priv,0))
 !PARSE-TREE:  DeclarationConstruct -> SpecificationConstruct -> OpenMPDeclarativeConstruct -> OpenMPDeclareReductionConstruct
 !PARSE-TREE: OmpReductionCombiner -> AssignmentStmt = 'omp_out=omp_out+omp_in'
-!PARSE-TREE:    OmpReductionInitializerClause -> OmpReductionInitializerProc
+!PARSE-TREE:    OmpInitializerClause -> OmpInitializerProc
 !PARSE-TREE-NEXT: ProcedureDesignator -> Name = 'initme'
   res=init
 !$omp simd reduction(red_add:res)
@@ -58,4 +58,4 @@ end program main
 !PARSE-TREE:        OmpReductionIdentifier -> ProcedureDesignator -> Name = 'my_add_red'
 !PARSE-TREE:        DeclarationTypeSpec -> IntrinsicTypeSpec -> IntegerTypeSpec
 !PARSE-TREE:        OmpReductionCombiner -> AssignmentStmt = 'omp_out=omp_out+omp_in'
-!PARSE-TREE:        OmpReductionInitializerClause -> OmpReductionInitializerExpr -> Expr = '0_4'
+!PARSE-TREE:        OmpInitializerClause -> OmpInitializerExpr -> Expr = '0_4'
diff --git a/llvm/include/llvm/Frontend/OpenMP/OMP.td b/llvm/include/llvm/Frontend/OpenMP/OMP.td
index 39fd46bcbd4ee..8a2f30a7995dc 100644
--- a/llvm/include/llvm/Frontend/OpenMP/OMP.td
+++ b/llvm/include/llvm/Frontend/OpenMP/OMP.td
@@ -244,6 +244,9 @@ def OMPC_Indirect : Clause<"indirect"> {
 def OMPC_Init : Clause<"init"> {
   let clangClass = "OMPInitClause";
 }
+def OMPC_Initializer : Clause<"initializer"> {
+  let flangClass = "OmpInitializerClause";
+}
 def OMPC_InReduction : Clause<"in_reduction"> {
   let clangClass = "OMPInReductionClause";
   let flangClass = "OmpInReductionClause";
@@ -668,6 +671,9 @@ def OMP_DeclareMapper : Directive<"declare mapper"> {
   let category = CA_Declarative;
 }
 def OMP_DeclareReduction : Directive<"declare reduction"> {
+  let allowedOnceClauses = [
+    VersionedClause<OMPC_Initializer>,
+  ];
   let association = AS_None;
   let category = CA_Declarative;
 }