diff --git a/src/compiler/code-generator.cc b/src/compiler/code-generator.cc
index bb0ef1bc19..d1faeb07f6 100644
--- a/src/compiler/code-generator.cc
+++ b/src/compiler/code-generator.cc
@@ -107,8 +107,7 @@ void CodeGenerator::AssembleInstruction(Instruction* instr) {
     if (FLAG_code_comments) {
       // TODO(titzer): these code comments are a giant memory leak.
       Vector<char> buffer = Vector<char>::New(32);
-      // TODO(dcarney): should not be rpo number there
-      SNPrintF(buffer, "-- B%d (rpo) start --", current_block_.ToInt());
+      SNPrintF(buffer, "-- B%d start --", block_start->id().ToInt());
       masm()->RecordComment(buffer.start());
     }
     masm()->bind(block_start->label());
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index 72ea0433d5..fc4778f894 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -598,6 +598,7 @@ class BlockStartInstruction FINAL : public GapInstruction {
  public:
   Label* label() { return &label_; }
   BasicBlock::RpoNumber rpo_number() const { return rpo_number_; }
+  BasicBlock::Id id() const { return id_; }
 
   static BlockStartInstruction* New(Zone* zone, BasicBlock* block) {
     void* buffer = zone->New(sizeof(BlockStartInstruction));
@@ -612,8 +613,10 @@ class BlockStartInstruction FINAL : public GapInstruction {
  private:
   explicit BlockStartInstruction(BasicBlock* block)
       : GapInstruction(kBlockStartInstruction),
+        id_(block->id()),
         rpo_number_(block->GetRpoNumber()) {}
 
+  BasicBlock::Id id_;
   BasicBlock::RpoNumber rpo_number_;
   Label label_;
 };