diff --git a/cmdline/snapraid.c b/cmdline/snapraid.c
index 86ad7a9c..10467af2 100644
--- a/cmdline/snapraid.c
+++ b/cmdline/snapraid.c
@@ -906,7 +906,7 @@ int parse_option_size(const char* arg, uint64_t* out_size)
 	char* e;
 
 	/* parse the number part */
-	data_off_t size = strtoul(optarg, &e, 10);
+	data_off_t size = strtoul(arg, &e, 10);
 	if (!e || e == arg)
 		return -1;