Index: lib/Sema/SemaOpenMP.cpp
===================================================================
--- lib/Sema/SemaOpenMP.cpp
+++ lib/Sema/SemaOpenMP.cpp
@@ -1997,6 +1997,8 @@
     if (isOpenMPTargetExecutionDirective(DKind) && !FD->isBitField()) {
       OMPClauseMappableExprCommon::MappableExprComponentList CurComponents;
       CheckMapClauseExpressionBase(SemaRef, E, CurComponents, OMPC_map);
+      if (CurComponents.empty())
+        return;
       auto *VD = cast<ValueDecl>(
           CurComponents.back().getAssociatedDeclaration()->getCanonicalDecl());
       if (!Stack->checkMappableExprComponentListsForDecl(
Index: test/OpenMP/target_map_messages.cpp
===================================================================
--- test/OpenMP/target_map_messages.cpp
+++ test/OpenMP/target_map_messages.cpp
@@ -269,6 +269,10 @@
   {}
   #pragma omp target map(u.B)  // expected-error {{mapped storage cannot be derived from a union}}
   {}
+  #pragma omp target
+  {
+    u.B = 0; // expected-error {{mapped storage cannot be derived from a union}}
+  }
 
   #pragma omp target data map(to: r.C) //expected-note {{used here}}
   {