diff --git a/lib/Checker/AttrNonNullChecker.cpp b/lib/Checker/AttrNonNullChecker.cpp
index d0bccb2..54b7b72 100644
--- a/lib/Checker/AttrNonNullChecker.cpp
+++ b/lib/Checker/AttrNonNullChecker.cpp
@@ -67,6 +67,28 @@
     if (!DV)
       continue;
 
+    if (!isa<Loc>(*DV)) {
+      // If the argument is a union type, we want to handle a potential
+      // transparent_unoin GCC extension.
+      QualType T = (*I)->getType();
+      const RecordType *UT = T->getAsUnionType();
+      if (!UT || !UT->getDecl()->hasAttr<TransparentUnionAttr>())
+        continue;
+      if (nonloc::CompoundVal *CSV = dyn_cast<nonloc::CompoundVal>(DV)) {
+        nonloc::CompoundVal::iterator CSV_I = CSV->begin();
+        assert(CSV_I != CSV->end());
+        V = *CSV_I;
+        DV = dyn_cast<DefinedSVal>(&V);
+        assert(++CSV_I == CSV->end());
+        if (!DV)
+          continue;        
+      }
+      else {
+        // FIXME: Handle LazyCompoundVals?
+        continue;
+      }
+    }
+
     ConstraintManager &CM = C.getConstraintManager();
     const GRState *stateNotNull, *stateNull;
     llvm::tie(stateNotNull, stateNull) = CM.AssumeDual(state, *DV);
diff --git a/test/Analysis/misc-ps-region-store.m b/test/Analysis/misc-ps-region-store.m
index ed285b4..0a6884b 100644
--- a/test/Analysis/misc-ps-region-store.m
+++ b/test/Analysis/misc-ps-region-store.m
@@ -1188,4 +1188,18 @@
   tmp2 = tmp2t[2];
 }
 
+// <rdar://problem/8642434> - Handle transparent unions with the AttrNonNullChecker.
+typedef union {
+  struct rdar_8642434_typeA *_dq;
+}
+rdar_8642434_typeB __attribute__((transparent_union));
+
+__attribute__((visibility("default"))) __attribute__((__nonnull__)) __attribute__((__nothrow__))
+void rdar_8642434_funcA(rdar_8642434_typeB object);
+
+void rdar_8642434_funcB(struct rdar_8642434_typeA *x, struct rdar_8642434_typeA *y) {
+  rdar_8642434_funcA(x);
+  if (!y)
+    rdar_8642434_funcA(y); // expected-warning{{Null pointer passed as an argument to a 'nonnull' parameter}}
+}