diff --git a/source/opt/basic_block.h b/source/opt/basic_block.h
index 0bab337147..6741a50f26 100644
--- a/source/opt/basic_block.h
+++ b/source/opt/basic_block.h
@@ -214,7 +214,7 @@ class BasicBlock {
   void KillAllInsts(bool killLabel);
 
   // Splits this basic block into two. Returns a new basic block with label
-  // |labelId| containing the instructions from |iter| onwards. Instructions
+  // |label_id| containing the instructions from |iter| onwards. Instructions
   // prior to |iter| remain in this basic block.  The new block will be added
   // to the function immediately after the original block.
   BasicBlock* SplitBasicBlock(IRContext* context, uint32_t label_id,