diff --git a/flang/lib/Semantics/check-omp-structure.h b/flang/lib/Semantics/check-omp-structure.h
--- a/flang/lib/Semantics/check-omp-structure.h
+++ b/flang/lib/Semantics/check-omp-structure.h
@@ -155,8 +155,10 @@
   void Enter(const parser::OmpClause::Reduction &);
   void Enter(const parser::OmpClause::Safelen &);
   void Enter(const parser::OmpClause::Shared &);
+  void Enter(const parser::OmpClause::Simd &);
   void Enter(const parser::OmpClause::Simdlen &);
   void Enter(const parser::OmpClause::TaskReduction &);
+  void Enter(const parser::OmpClause::Threads &);
   void Enter(const parser::OmpClause::ThreadLimit &);
   void Enter(const parser::OmpClause::To &);
   void Enter(const parser::OmpClause::Link &);
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
@@ -433,6 +433,8 @@
 CHECK_SIMPLE_CLAUSE(Hint, OMPC_hint)
 CHECK_SIMPLE_CLAUSE(ProcBind, OMPC_proc_bind)
 CHECK_SIMPLE_CLAUSE(DistSchedule, OMPC_dist_schedule)
+CHECK_SIMPLE_CLAUSE(Simd, OMPC_simd)
+CHECK_SIMPLE_CLAUSE(Threads, OMPC_threads)
 
 CHECK_REQ_SCALAR_INT_CLAUSE(Allocator, OMPC_allocator)
 CHECK_REQ_SCALAR_INT_CLAUSE(Grainsize, OMPC_grainsize)
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
@@ -485,6 +485,14 @@
   !$omp ordered depend(source)
   !ERROR: Internal: no symbol found for 'i'
   !$omp ordered depend(sink:i-1)
+  !ERROR: At most one DEPEND clause can appear on the ORDERED directive
+  !$omp ordered depend(source) depend(source)
+  !ERROR: At most one THREADS clause can appear on the ORDERED directive
+  !$omp ordered threads threads
+  !$omp end ordered
+  !ERROR: At most one SIMD clause can appear on the ORDERED directive
+  !$omp ordered simd simd
+  !$omp end ordered
   !$omp flush (c)
   !$omp flush acq_rel
   !$omp flush release
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
@@ -455,7 +455,7 @@
   ];
 }
 def OMP_Ordered : Directive<"ordered"> {
-  let allowedClauses = [
+  let allowedOnceClauses = [
     VersionedClause<OMPC_Threads>,
     VersionedClause<OMPC_Simd>,
     VersionedClause<OMPC_Depend>