diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index c550e68..aeacfd5 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1095,10 +1095,11 @@
     SrcBits = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(3))->getVT());
     return (Mask & ((1ULL << SrcBits)-1)) == 0; // Returning only the zext bits.
   case ISD::ZERO_EXTEND:
-  case ISD::AssertZext:
     SrcBits = MVT::getSizeInBits(Op.getOperand(0).getValueType());
     return MaskedValueIsZero(Op.getOperand(0),Mask & ((1ULL << SrcBits)-1),TLI);
-
+  case ISD::AssertZext:
+    SrcBits = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(1))->getVT());
+    return (Mask & ((1ULL << SrcBits)-1) == 0; // Returning only the zext bits.
   case ISD::AND:
     // (X & C1) & C2 == 0   iff   C1 & C2 == 0.
     if (ConstantSDNode *AndRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1)))