diff --git a/github/review.go b/github/review.go
index 1d043e5..29e1639 100644
--- a/github/review.go
+++ b/github/review.go
@@ -103,7 +103,7 @@ func (c *Client) PostReview(ctx context.Context, owner, repo string, number int,
 	// the resolved commit_id.
 	for _, comment := range req.Comments {
 		if comment.CommitID != "" {
-			if payload.CommitID == "" {
+			if payload.CommitID == "" { // only reachable when req.CommitID is empty
 				payload.CommitID = comment.CommitID
 			} else if payload.CommitID != comment.CommitID {
 				return nil, ErrConflictingCommitIDs