diff --git a/apps/x509.c b/apps/x509.c
index aa06462b9f41b3c506ccab6a4fd1f6afeaa2b35e..12b269f9ab70a29e4298f430f8dbc841d1d1ebac 100644
--- a/apps/x509.c
+++ b/apps/x509.c
@@ -122,7 +122,7 @@ static char *x509_usage[]={
 " -CAkey arg      - set the CA key, must be PEM format\n",
 "                   missing, it is assumed to be in the CA file.\n",
 " -CAcreateserial - create serial number file if it does not exist\n",
-" -CAserial       - serial file\n",
+" -CAserial arg   - serial file\n",
 " -set_serial     - serial number to use\n",
 " -text           - print the certificate in text form\n",
 " -C              - print out C code forms\n",