diff --git a/lib/Analysis/GRSimpleVals.cpp b/lib/Analysis/GRSimpleVals.cpp
index c1f455b..d50876e 100644
--- a/lib/Analysis/GRSimpleVals.cpp
+++ b/lib/Analysis/GRSimpleVals.cpp
@@ -74,6 +74,11 @@
   if (Loc::IsLocType(T) || T->isReferenceType())
     return X;
   
+  // FIXME: Handle transparent unions where a value can be "transparently"
+  //  lifted into a union type.
+  if (T->isUnionType())
+    return UnknownVal();
+  
   assert (T->isIntegerType());
   BasicValueFactory& BasicVals = Eng.getBasicVals();
   unsigned BitWidth = Eng.getContext().getTypeSize(T);