diff --git a/src/sample.c b/src/sample.c
index bb7db28e7..57cb7c6f8 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -3155,7 +3155,10 @@ static int check_operator(struct arg *args, struct sample_conv *conv,
 	const char *end;
 	long long int i;
 
-	/* Try to decode a variable. */
+	/* Try to decode a variable. The 'err' variable is intentionnaly left
+	 * NULL since the operators accept an integer as argument in which case
+	 * vars_check_arg call will fail.
+	 */
 	if (vars_check_arg(&args[0], NULL))
 		return 1;