diff --git a/lib/CodeGen/CGRecordLayoutBuilder.cpp b/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 74fd794..537daf9 100644
--- a/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -997,7 +997,7 @@
 
   // If we're in C++, compute the base subobject type.
   llvm::StructType *BaseTy = 0;
-  if (isa<CXXRecordDecl>(D)) {
+  if (isa<CXXRecordDecl>(D) && !D->isUnion()) {
     BaseTy = Builder.BaseSubobjectType;
     if (!BaseTy) BaseTy = Ty;
   }