diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 66356f5..358c970 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2008,7 +2008,7 @@
     if (Tmp == 1) return 1;  // Early out.
 
     // Special case decrementing a value (ADD X, -1):
-    if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(0)))
+    if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
       if (CRHS->isAllOnesValue()) {
         APInt KnownZero, KnownOne;
         APInt Mask = APInt::getAllOnesValue(VTBits);