diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 19bc7f9..ae97b24 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7202,6 +7202,11 @@
           dyn_cast<CXXRecordDecl>(NewFD->getDeclContext())) {
       if (Parent->isInterface() && cast<CXXMethodDecl>(NewFD)->isUserProvided())
         NewFD->setPure(true);
+
+      // C++ [class.union]p2
+      //   A union can have member functions, but not virtual functions.
+      if (isVirtual && Parent->isUnion())
+        Diag(D.getDeclSpec().getVirtualSpecLoc(), diag::err_virtual_in_union);
     }
 
     SetNestedNameSpecifier(NewFD, D);