diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index 6734916..b4a2ca1 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/lib/CodeGen/MachineBasicBlock.cpp
@@ -870,11 +870,11 @@
 
 /// getSuccWeight - Return weight of the edge from this block to MBB.
 ///
-uint32_t MachineBasicBlock::getSuccWeight(MachineBasicBlock *succ) {
+uint32_t MachineBasicBlock::getSuccWeight(const MachineBasicBlock *succ) const {
   if (Weights.empty())
     return 0;
 
-  succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
+  const_succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
   return *getWeightIterator(I);
 }
 
@@ -888,6 +888,16 @@
   return Weights.begin() + index;
 }
 
+/// getWeightIterator - Return wight iterator corresonding to the I successor
+/// iterator
+MachineBasicBlock::const_weight_iterator MachineBasicBlock::
+getWeightIterator(MachineBasicBlock::const_succ_iterator I) const {
+  assert(Weights.size() == Successors.size() && "Async weight list!");
+  const size_t index = std::distance(Successors.begin(), I);
+  assert(index < Weights.size() && "Not a current successor!");
+  return Weights.begin() + index;
+}
+
 void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
                           bool t) {
   OS << "BB#" << MBB->getNumber();