diff --git a/include/llvm/CodeGen/MachineFunction.h b/include/llvm/CodeGen/MachineFunction.h
index 1c9bc61521f..a110e5846ac 100644
--- a/include/llvm/CodeGen/MachineFunction.h
+++ b/include/llvm/CodeGen/MachineFunction.h
@@ -176,7 +176,7 @@ public:
   /// basic block can be found by using the MBB::getBlockNumber method, this
   /// method provides the inverse mapping.
   ///
-  MachineBasicBlock *getBlockNumbered(unsigned N) {
+  MachineBasicBlock *getBlockNumbered(unsigned N) const {
     assert(N < MBBNumbering.size() && "Illegal block number");
     assert(MBBNumbering[N] && "Block was removed from the machine function!");
     return MBBNumbering[N];