diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index ba9be6a..2cafbd4 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -1064,6 +1064,8 @@
 unsigned MachineInstr::isConstantValuePHI() const {
   if (getOpcode() != TargetInstrInfo::PHI)
     return 0;
+  if (getNumOperands() <= 1)
+    return 0;
 
   unsigned Reg = getOperand(1).getReg();
   for (unsigned i = 3, e = getNumOperands(); i < e; i += 2)