diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index f26bf47a5bae2089d1d0c8ed5d91a06785423778..25165bae48fa612db6cf01b221fda5803ee9cda1 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8318,6 +8318,9 @@ def err_omp_expected_int_param : Error<
   "expected a reference to an integer-typed parameter">;
 def err_omp_at_least_one_motion_clause_required : Error<
   "expected at least one 'to' clause or 'from' clause specified to '#pragma omp target update'">;
+def warn_omp_nesting_simd : Warning<
+  "OpenMP only allows an ordered construct with the simd clause nested in a simd construct">,
+  InGroup<SourceUsesOpenMP>;
 } // end of OpenMP category
 
 let CategoryName = "Related Result Type Issue" in {
diff --git a/lib/Sema/SemaOpenMP.cpp b/lib/Sema/SemaOpenMP.cpp
index 21ccfd047890884146bc4987d6c669d59e48304f..ec67bcaf88178670bf7829f9785547a3836b88c6 100644
--- a/lib/Sema/SemaOpenMP.cpp
+++ b/lib/Sema/SemaOpenMP.cpp
@@ -2940,15 +2940,19 @@ static bool CheckNestingOfRegions(Sema &SemaRef, DSAStackTy *Stack,
       ShouldBeInTargetRegion,
       ShouldBeInTeamsRegion
     } Recommend = NoRecommend;
-    if (isOpenMPSimdDirective(ParentRegion) && CurrentRegion != OMPD_ordered &&
-        CurrentRegion != OMPD_simd) {
+    if (isOpenMPSimdDirective(ParentRegion) && CurrentRegion != OMPD_ordered) {
       // OpenMP [2.16, Nesting of Regions]
       // OpenMP constructs may not be nested inside a simd region.
       // OpenMP [2.8.1,simd Construct, Restrictions]
-      // An ordered construct with the simd clause is the only OpenMP construct
-      // that can appear in the simd region.
-      SemaRef.Diag(StartLoc, diag::err_omp_prohibited_region_simd);
-      return true;
+      // An ordered construct with the simd clause is the only OpenMP
+      // construct that can appear in the simd region.
+      // Allowing a SIMD consruct nested in another SIMD construct is an
+      // extension. The OpenMP 4.5 spec does not allow it. Issue a warning
+      // message.
+      SemaRef.Diag(StartLoc, (CurrentRegion != OMPD_simd)
+                                 ? diag::err_omp_prohibited_region_simd
+                                 : diag::warn_omp_nesting_simd);
+      return CurrentRegion != OMPD_simd;
     }
     if (ParentRegion == OMPD_atomic) {
       // OpenMP [2.16, Nesting of Regions]
diff --git a/test/OpenMP/nesting_of_regions.cpp b/test/OpenMP/nesting_of_regions.cpp
index 38012e85961a373a0dfdba8b4bbd1c44f9c6e98a..3694aa9fb4bcbfd6458b5c2c7453bdcff4bcc5bc 100644
--- a/test/OpenMP/nesting_of_regions.cpp
+++ b/test/OpenMP/nesting_of_regions.cpp
@@ -153,7 +153,7 @@ void foo() {
   }
 #pragma omp simd
   for (int i = 0; i < 10; ++i) {
-#pragma omp simd
+#pragma omp simd // expected-warning {{OpenMP only allows an ordered construct with the simd clause nested in a simd construct}}
     for (int i = 0; i < 10; ++i)
       ;
   }
@@ -257,6 +257,16 @@ void foo() {
   }
 #pragma omp simd
   for (int i = 0; i < 10; ++i) {
+#pragma omp ordered simd // OK
+    bar();
+  }
+#pragma omp simd
+  for (int i = 0; i < 10; ++i) {
+#pragma omp ordered threads // expected-error {{OpenMP constructs may not be nested inside a simd region}}
+    bar();
+  }
+#pragma omp simd
+  for (int i = 0; i < 10; ++i) {
 #pragma omp atomic // expected-error {{OpenMP constructs may not be nested inside a simd region}}
     ++a;
   }
@@ -516,7 +526,7 @@ void foo() {
   }
 #pragma omp for simd
   for (int i = 0; i < 10; ++i) {
-#pragma omp simd
+#pragma omp simd // expected-warning {{OpenMP only allows an ordered construct with the simd clause nested in a simd construct}}
     for (int i = 0; i < 10; ++i)
       ;
   }
@@ -620,6 +630,16 @@ void foo() {
   }
 #pragma omp for simd
   for (int i = 0; i < 10; ++i) {
+#pragma omp ordered simd // OK
+    bar();
+  }
+#pragma omp for simd
+  for (int i = 0; i < 10; ++i) {
+#pragma omp ordered threads // expected-error {{OpenMP constructs may not be nested inside a simd region}}
+    bar();
+  }
+#pragma omp for simd
+  for (int i = 0; i < 10; ++i) {
 #pragma omp atomic // expected-error {{OpenMP constructs may not be nested inside a simd region}}
     ++a;
   }
@@ -1902,7 +1922,7 @@ void foo() {
   }
 #pragma omp parallel for simd
   for (int i = 0; i < 10; ++i) {
-#pragma omp simd
+#pragma omp simd // expected-warning {{OpenMP only allows an ordered construct with the simd clause nested in a simd construct}}
     for (int i = 0; i < 10; ++i)
       ;
   }
@@ -4314,7 +4334,7 @@ void foo() {
   }
 #pragma omp simd
   for (int i = 0; i < 10; ++i) {
-#pragma omp simd
+#pragma omp simd // expected-warning {{OpenMP only allows an ordered construct with the simd clause nested in a simd construct}}
     for (int i = 0; i < 10; ++i)
       ;
   }
@@ -4662,7 +4682,7 @@ void foo() {
   }
 #pragma omp for simd
   for (int i = 0; i < 10; ++i) {
-#pragma omp simd
+#pragma omp simd // expected-warning {{OpenMP only allows an ordered construct with the simd clause nested in a simd construct}}
     for (int i = 0; i < 10; ++i)
       ;
   }
@@ -6022,7 +6042,7 @@ void foo() {
   }
 #pragma omp parallel for simd
   for (int i = 0; i < 10; ++i) {
-#pragma omp simd
+#pragma omp simd // expected-warning {{OpenMP only allows an ordered construct with the simd clause nested in a simd construct}}
     for (int i = 0; i < 10; ++i)
       ;
   }