diff --git a/llvm/lib/CodeGen/RDFGraph.cpp b/llvm/lib/CodeGen/RDFGraph.cpp
index 6276a4722e3f0..ff0fd61078c0b 100644
--- a/llvm/lib/CodeGen/RDFGraph.cpp
+++ b/llvm/lib/CodeGen/RDFGraph.cpp
@@ -264,7 +264,7 @@ raw_ostream &operator<<(raw_ostream &OS, const Print<Block> &P) {
   MachineBasicBlock *BB = P.Obj.Addr->getCode();
   unsigned NP = BB->pred_size();
   std::vector<int> Ns;
-  auto PrintBBs = [&OS](std::vector<int> Ns) -> void {
+  auto PrintBBs = [&OS](const std::vector<int> &Ns) -> void {
     unsigned N = Ns.size();
     for (int I : Ns) {
       OS << "%bb." << I;