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
@@ -667,6 +667,7 @@
 CHECK_SIMPLE_CLAUSE(Relaxed, OMPC_relaxed)
 CHECK_SIMPLE_CLAUSE(SeqCst, OMPC_seq_cst)
 CHECK_SIMPLE_CLAUSE(Simd, OMPC_simd)
+CHECK_SIMPLE_CLAUSE(Sizes, OMPC_sizes)
 CHECK_SIMPLE_CLAUSE(TaskReduction, OMPC_task_reduction)
 CHECK_SIMPLE_CLAUSE(To, OMPC_to)
 CHECK_SIMPLE_CLAUSE(UnifiedAddress, OMPC_unified_address)