diff --git a/README b/README
index af6a84c..1270d45 100644
--- a/README
+++ b/README
@@ -19,11 +19,12 @@ from sandbox/cdba/cdba-server. Available devices are read from $HOME/.cdba
 = Client side
 The client is invoked as:
 
-  cdba -b <board> -h <host> [-c <power-cylce-count>] [-s <status-fifo>] boot.img
+  cdba -b <board> -h <host> [-c <power-cylce-count>] [-s <status-fifo>] [boot.img]
 
 <host> will be connected to using ssh and <board> will be selected for
-operation. As the board's fastboot interface shows up the given boot.img will
-be transfered and booted on the device.
+operation. As the board's fastboot interface shows up the given boot.img
+will be transfered and booted on the device. If [boot.img] is omitted,
+"fastboot continue" is run to boot the installed operating system.
 
 The board will execute until the key sequence ^A q is invoked or the board
 outputs a sequence of 20 ~ (tilde) chards in a row.
diff --git a/cdba.c b/cdba.c
index ee3809f..a526fad 100644
--- a/cdba.c
+++ b/cdba.c
@@ -584,7 +584,7 @@ static void usage(void)
 	extern const char *__progname;
 
 	fprintf(stderr, "usage: %s -b <board> -h <host> [-t <timeout>] "
-			"[-T <inactivity-timeout>] <boot.img>\n",
+			"[-T <inactivity-timeout>] [boot.img]\n",
 			__progname);
 	fprintf(stderr, "usage: %s -i -b <board> -h <host>\n",
 			__progname);