diff --git a/lib/CodeGen/RegAllocSimple.cpp b/lib/CodeGen/RegAllocSimple.cpp
index cd48cd2..1b7f547 100644
--- a/lib/CodeGen/RegAllocSimple.cpp
+++ b/lib/CodeGen/RegAllocSimple.cpp
@@ -172,7 +172,8 @@
     for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
       MachineOperand &op = MI->getOperand(i);
       
-      if (op.isRegister() && MRegisterInfo::isVirtualRegister(op.getReg())) {
+      if (op.isRegister() && op.getReg() &&
+          MRegisterInfo::isVirtualRegister(op.getReg())) {
         unsigned virtualReg = (unsigned) op.getReg();
         DEBUG(std::cerr << "op: " << op << "\n");
         DEBUG(std::cerr << "\t inst[" << i << "]: ";