diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -208,7 +208,16 @@
   PushContextAndClauseSets(dir.source, llvm::omp::Directive::OMPD_flush);
 }
 
-void OmpStructureChecker::Leave(const parser::OpenMPFlushConstruct &) {
+void OmpStructureChecker::Leave(const parser::OpenMPFlushConstruct &x) {
+  if (FindClause(llvm::omp::Clause::OMPC_acquire) ||
+      FindClause(llvm::omp::Clause::OMPC_release) ||
+      FindClause(llvm::omp::Clause::OMPC_acq_rel)) {
+    if (const auto &flushList{
+            std::get<std::optional<parser::OmpObjectList>>(x.t)}) {
+      context_.Say(parser::FindSourceLocation(flushList),
+          "If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive"_err_en_US);
+    }
+  }
   dirContext_.pop_back();
 }
 
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
@@ -487,6 +487,7 @@
   !$omp flush acq_rel
   !$omp flush release
   !$omp flush acquire
+  !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
   !$omp flush release (c)
   !ERROR: SEQ_CST clause is not allowed on the FLUSH directive
   !$omp flush seq_cst
diff --git a/flang/test/Semantics/omp-flush01.f90 b/flang/test/Semantics/omp-flush01.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-flush01.f90
@@ -0,0 +1,53 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+
+! 2.17.8 Flush construct [OpenMP 5.0]
+!        memory-order-clause ->
+!                               acq_rel
+!                               release
+!                               acquire
+use omp_lib
+  implicit none
+
+  integer :: i, a, b
+  real, DIMENSION(10) :: array
+
+  a = 1.0
+  !$omp parallel num_threads(4)
+  !Only memory-order-clauses.
+  if (omp_get_thread_num() == 1) then
+    ! Allowed clauses.
+    !$omp flush acq_rel
+    array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+    !$omp flush release
+    array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+    !$omp flush acquire
+
+    ! Not allowed more than once.
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush acq_rel acq_rel
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush release release
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush acquire acquire
+
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush private(array)
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush num_threads(4)
+
+    ! Mix allowed and not allowed clauses.
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush seq_cst acquire
+    !ERROR: expected end of line
+    !ERROR: expected end of line
+    !$omp flush num_threads(4) acquire
+  end if
+  !$omp end parallel
+end
+
diff --git a/flang/test/Semantics/omp-flush02.f90 b/flang/test/Semantics/omp-flush02.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-flush02.f90
@@ -0,0 +1,75 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+
+! Check OpenMP 5.0 - 2.17.8 flush Construct
+! Restriction -
+! If memory-order-clause is release, acquire, or acq_rel, list items must not be specified on the flush directive.
+
+use omp_lib
+  implicit none
+
+  TYPE someStruct
+    REAL :: rr
+  end TYPE
+  integer :: i, a, b
+  real, DIMENSION(10) :: array
+  TYPE(someStruct) :: structObj
+
+  a = 1.0
+  !$omp parallel num_threads(4)
+  !No list flushes all.
+  if (omp_get_thread_num() == 1) THEN
+    !$omp flush
+  END IF
+
+  array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+  !Only memory-order-clauses.
+  if (omp_get_thread_num() == 1) THEN
+    ! Not allowed clauses.
+    !ERROR: SEQ_CST clause is not allowed on the FLUSH directive
+    !$omp flush seq_cst
+
+    !ERROR: RELAXED clause is not allowed on the FLUSH directive
+    !$omp flush relaxed
+  END IF
+
+  array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+  ! No memory-order-clause only list-items.
+  if (omp_get_thread_num() == 2) THEN
+    !$omp flush (a)
+    !$omp flush (i, a, b)
+    !$omp flush (array, structObj%rr)
+    ! Too many flush with repeating list items.
+    !$omp flush (i, a, b, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, b, b, b, b)
+    !ERROR: No explicit type declared for 'notpresentitem'
+    !$omp flush (notPresentItem)
+  END IF
+
+  array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+  if (omp_get_thread_num() == 3) THEN
+    !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
+    !$omp flush acq_rel (array)
+    !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
+    !$omp flush acq_rel (array, a, i)
+
+    array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+    !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
+    !$omp flush release (array)
+    !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
+    !$omp flush release (array, a)
+
+    array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+    !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
+    !$omp flush acquire (array)
+    !ERROR: If memory-order-clause is RELEASE, ACQUIRE, or ACQ_REL, list items must not be specified on the FLUSH directive
+    !$omp flush acquire (array, a, structObj%rr)
+  END IF
+  !$omp end parallel
+
+  !$omp parallel num_threads(4)
+    array = (/1, 2, 3, 4, 5, 6, 7, 8, 9, 10/)
+    !$omp master
+      !$omp flush (array)
+    !$omp end master
+  !$omp end parallel
+end
+