Index: flang/lib/Semantics/check-omp-structure.h
===================================================================
--- flang/lib/Semantics/check-omp-structure.h
+++ flang/lib/Semantics/check-omp-structure.h
@@ -231,6 +231,7 @@
       const parser::CharBlock &source, const parser::OmpCancelType::Type &type);
   std::int64_t GetOrdCollapseLevel(const parser::OpenMPLoopConstruct &x);
   void CheckIfDoOrderedClause(const parser::OmpBlockDirective &blkDirectiv);
+  void CheckAllowedOnceClause(const llvm::omp::Clause);
   bool CheckReductionOperators(const parser::OmpClause::Reduction &);
   bool CheckIntrinsicOperator(
       const parser::DefinedOperator::IntrinsicOperator &);
Index: flang/lib/Semantics/check-omp-structure.cpp
===================================================================
--- flang/lib/Semantics/check-omp-structure.cpp
+++ flang/lib/Semantics/check-omp-structure.cpp
@@ -759,6 +759,22 @@
   }
 }
 
+void OmpStructureChecker::CheckAllowedOnceClause(
+    const llvm::omp::Clause clause) {
+  auto clauseAll = FindClauses(clause);
+  unsigned clauseCnt = 0;
+  for (auto itr = clauseAll.first; itr != clauseAll.second; ++itr) {
+    clauseCnt++;
+    if (clauseCnt > 1) {
+      context_.Say(itr->second->source,
+          "At most one %s clause can appear on the %s directive"_err_en_US,
+          parser::ToUpperCaseLetters(getClauseName(clause).str()),
+          ContextDirectiveAsFortran());
+      break;
+    }
+  }
+}
+
 void OmpStructureChecker::Leave(const parser::OpenMPBlockConstruct &) {
   if (GetDirectiveNest(TargetBlockOnlyTeams)) {
     ExitDirectiveNest(TargetBlockOnlyTeams);
@@ -1238,6 +1254,30 @@
         llvm::omp::Clause::OMPC_copyprivate, {llvm::omp::Clause::OMPC_nowait});
   }
 
+  // 2.19.9 Ordered Construct Restriction
+  if (GetContext().directive == llvm::omp::Directive::OMPD_ordered) {
+    // At most one threads clause can appear on an ordered construct.
+    CheckAllowedOnceClause(llvm::omp::Clause::OMPC_threads);
+    // At most one simd clause can appear on an ordered construct.
+    CheckAllowedOnceClause(llvm::omp::Clause::OMPC_simd);
+    // At most one depend(source) clause can appear on an ordered construct.
+    auto clauseAll = FindClauses(llvm::omp::Clause::OMPC_depend);
+    unsigned dependSourceCnt = 0;
+    for (auto itr = clauseAll.first; itr != clauseAll.second; ++itr) {
+      const auto &dependClause{
+          std::get<parser::OmpClause::Depend>(itr->second->u)};
+      if (std::get_if<parser::OmpDependClause::Source>(&dependClause.v.u)) {
+        dependSourceCnt++;
+        if (dependSourceCnt > 1) {
+          context_.Say(itr->second->source,
+              "At most one DEPEND(SOURCE) clause can appear on the ORDERED "
+              "directive"_err_en_US);
+          break;
+        }
+      }
+    }
+  }
+
   CheckRequireAtLeastOneOf();
 }
 
Index: flang/test/Semantics/omp-ordered01.f90
===================================================================
--- /dev/null
+++ flang/test/Semantics/omp-ordered01.f90
@@ -0,0 +1,49 @@
+! RUN: %S/test_errors.sh %s %t %flang_fc1 -fopenmp
+! REQUIRES: shell
+
+! OpenMP Version 5.1
+! Check OpenMP construct validity for the following directives:
+! 2.19.9 Ordered Construct
+
+program main
+  integer :: i, N = 10
+  real :: a, arrayA(10), arrayB(10)
+  real, external :: foo, bar
+
+  !$omp do ordered
+  do i = 1, N
+    !ERROR: At most one THREADS clause can appear on the ORDERED directive
+    !$omp ordered threads threads
+    arrayA(i) = i
+    !$omp end ordered
+  end do
+  !$omp end do
+
+  !$omp simd
+  do i = 1, N
+    !ERROR: At most one SIMD clause can appear on the ORDERED directive
+    !$omp ordered simd simd
+    arrayA(i) = i
+    !$omp end ordered
+  end do
+  !$omp end simd
+
+  !$omp do simd ordered
+  do i = 1, N
+    !ERROR: At most one SIMD clause can appear on the ORDERED directive
+    !$omp ordered simd simd
+    arrayA(i) = i
+    !$omp end ordered
+  end do
+  !$omp end do simd
+
+  !$omp do ordered(1)
+  do i = 1, N
+    arrayA(i) = foo(i)
+    !ERROR: At most one DEPEND(SOURCE) clause can appear on the ORDERED directive
+    !$omp ordered depend(source) depend(source)
+    arrayB(i) = bar(arrayA(i))
+  end do
+  !$omp end do
+
+end program main