diff --git a/include/llvm/CodeGen/MachineRegisterInfo.h b/include/llvm/CodeGen/MachineRegisterInfo.h
index fd7431ff0bc..dede05f85c0 100644
--- a/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -216,7 +216,8 @@ public:
 
   /// getRegClassVirtRegs - Return the list of virtual registers of the given
   /// target register class.
-  std::vector<unsigned> &getRegClassVirtRegs(const TargetRegisterClass *RC) {
+  const std::vector<unsigned> &
+  getRegClassVirtRegs(const TargetRegisterClass *RC) const {
     return RegClass2VRegMap[RC->getID()];
   }
 
diff --git a/lib/CodeGen/PreAllocSplitting.cpp b/lib/CodeGen/PreAllocSplitting.cpp
index eb19be12cee..997e82f11db 100644
--- a/lib/CodeGen/PreAllocSplitting.cpp
+++ b/lib/CodeGen/PreAllocSplitting.cpp
@@ -1154,7 +1154,7 @@ PreAllocSplitting::SplitRegLiveIntervals(const TargetRegisterClass **RCs,
     // codegen is not modelling. Ignore these barriers for now.
     if (!TII->isSafeToMoveRegClassDefs(*RC))
       continue;
-    std::vector<unsigned> &VRs = MRI->getRegClassVirtRegs(*RC);
+    const std::vector<unsigned> &VRs = MRI->getRegClassVirtRegs(*RC);
     for (unsigned i = 0, e = VRs.size(); i != e; ++i) {
       unsigned Reg = VRs[i];
       if (!LIs->hasInterval(Reg))