diff --git a/flang/include/flang/Parser/dump-parse-tree.h b/flang/include/flang/Parser/dump-parse-tree.h
--- a/flang/include/flang/Parser/dump-parse-tree.h
+++ b/flang/include/flang/Parser/dump-parse-tree.h
@@ -514,6 +514,7 @@
   NODE(parser, OmpProcBindClause)
   NODE_ENUM(OmpProcBindClause, Type)
   NODE(parser, OmpReductionClause)
+  NODE(parser, OmpInReductionClause)
   NODE(parser, OmpReductionCombiner)
   NODE(OmpReductionCombiner, FunctionCombiner)
   NODE(parser, OmpReductionInitializerClause)
diff --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -3433,6 +3433,13 @@
   std::tuple<OmpReductionOperator, OmpObjectList> t;
 };
 
+// OMP 5.0 2.19.5.6 in-reduction-clause -> IN_REDUCTION (reduction-identifier:
+//                                                      variable-name-list)
+struct OmpInReductionClause {
+  TUPLE_CLASS_BOILERPLATE(OmpInReductionClause);
+  std::tuple<OmpReductionOperator, OmpObjectList> t;
+};
+
 // OMP 5.0 2.11.4 allocate-clause -> ALLOCATE ([allocator:] variable-name-list)
 struct OmpAllocateClause {
   TUPLE_CLASS_BOILERPLATE(OmpAllocateClause);
diff --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -104,6 +104,10 @@
 TYPE_PARSER(construct<OmpReductionClause>(
     Parser<OmpReductionOperator>{} / ":", Parser<OmpObjectList>{}))
 
+// OMP 5.0 2.19.5.6 IN_REDUCTION (reduction-identifier: variable-name-list)
+TYPE_PARSER(construct<OmpInReductionClause>(
+    Parser<OmpReductionOperator>{} / ":", Parser<OmpObjectList>{}))
+
 // OMP 5.0 2.11.4  ALLOCATE ([allocator:] variable-name-list)
 TYPE_PARSER(construct<OmpAllocateClause>(
     maybe(construct<OmpAllocateClause::Allocator>(scalarIntExpr) / ":"),
@@ -224,6 +228,8 @@
                        parenthesized(Parser<OmpProcBindClause>{}))) ||
     "REDUCTION" >> construct<OmpClause>(construct<OmpClause::Reduction>(
                        parenthesized(Parser<OmpReductionClause>{}))) ||
+    "IN_REDUCTION" >> construct<OmpClause>(construct<OmpClause::InReduction>(
+                          parenthesized(Parser<OmpInReductionClause>{}))) ||
     "TASK_REDUCTION" >>
         construct<OmpClause>(construct<OmpClause::TaskReduction>(
             parenthesized(Parser<OmpReductionClause>{}))) ||
diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -2025,6 +2025,11 @@
     Put(":");
     Walk(std::get<OmpObjectList>(x.t));
   }
+  void Unparse(const OmpInReductionClause &x) {
+    Walk(std::get<OmpReductionOperator>(x.t));
+    Put(":");
+    Walk(std::get<OmpObjectList>(x.t));
+  }
   void Unparse(const OmpAllocateClause &x) {
     Walk(std::get<std::optional<OmpAllocateClause::Allocator>>(x.t));
     Put(":");
diff --git a/flang/test/Parser/omp-block-construct-unparse.f90 b/flang/test/Parser/omp-block-construct-unparse.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Parser/omp-block-construct-unparse.f90
@@ -0,0 +1,11 @@
+! RUN: %flang_fc1 -fdebug-unparse-no-sema -fopenmp %s | FileCheck %s
+! Checks the unparsing of different OpenMP block constructs
+
+program block_construct_unparsing
+    integer:: x, y
+    !TASK
+    !CHECK: !$OMP TASK  IN_REDUCTION(+:x)
+    !CHECK: !$OMP END TASK
+    !$omp task in_reduction(+: x)
+    !$omp end task
+end program block_construct_unparsing
diff --git a/flang/test/Semantics/omp-clause-validity01.f90 b/flang/test/Semantics/omp-clause-validity01.f90
--- a/flang/test/Semantics/omp-clause-validity01.f90
+++ b/flang/test/Semantics/omp-clause-validity01.f90
@@ -61,7 +61,7 @@
   enddo
   !$omp end parallel
 
-  !$omp task private(b) allocate(b)
+  !$omp task private(b) allocate(b) in_reduction(+:b)
   do i = 1, N
      z = 2
   end do
diff --git a/llvm/include/llvm/Frontend/OpenMP/OMP.td b/llvm/include/llvm/Frontend/OpenMP/OMP.td
--- a/llvm/include/llvm/Frontend/OpenMP/OMP.td
+++ b/llvm/include/llvm/Frontend/OpenMP/OMP.td
@@ -264,6 +264,7 @@
 }
 def OMPC_InReduction : Clause<"in_reduction"> {
   let clangClass = "OMPInReductionClause";
+  let flangClass = "OmpInReductionClause";
 }
 def OMPC_UnifiedAddress : Clause<"unified_address"> {
   let clangClass = "OMPUnifiedAddressClause";