diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.def b/clang/include/clang/Basic/DiagnosticSemaKinds.def
index 7ebb5a706cda5934b535cc6c8471bdb3bb506ff8..fb9f36399baf1c088730eb028ea5f58c64e47f07 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.def
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.def
@@ -728,7 +728,7 @@ DIAG(err_field_declared_as_function, ERROR,
      "field %0 declared as a function")
 DIAG(err_field_incomplete, ERROR,
      "field has incomplete type %0")
-DIAG(err_variable_sized_type_in_struct, EXTENSION,
+DIAG(err_variable_sized_type_in_struct, ERROR,
      "variable sized type %0 must be at end of struct or class")
 DIAG(err_flexible_array_empty_struct, ERROR,
      "flexible array %0 not allowed in otherwise empty struct")
diff --git a/clang/test/Sema/struct-decl.c b/clang/test/Sema/struct-decl.c
index cdc9eaae3bbd336f4afc83130effb1bce86a9f56..aa2d3b6342b696c8cbe0864661c184d407882059 100644
--- a/clang/test/Sema/struct-decl.c
+++ b/clang/test/Sema/struct-decl.c
@@ -22,3 +22,14 @@ int foo() {
         struct st *f;
         return f->v + f[0].v;
 }
+
+// PR3642
+struct pppoe_tag {
+ short tag_type;
+ char tag_data[];
+};
+struct datatag {
+ struct pppoe_tag hdr; //expected-error{{variable sized type 'hdr' must be at end of struct}}
+ char data;
+};
+