diff --git a/README b/README
index e18294d..62d1726 100755
--- a/README
+++ b/README
@@ -1,4 +1,4 @@
-usage : tty-clock [-sctrvih] [-C [0-7]] [-f format]
+usage : tty-clock [-sctrvih] [-C [0-7]] [-f format] [-d delay]
     -s            Show seconds
     -c            Set the clock at the center of the terminal
     -C [0-7]      Set the clock color
@@ -8,3 +8,4 @@ usage : tty-clock [-sctrvih] [-C [0-7]] [-f format]
     -v            Show tty-clock version
     -i            Show some info about tty-clock
     -h            Show this page
+    -d delay      Set the delay between two redraws of the clock
diff --git a/ttyclock.c b/ttyclock.c
index 19a9d27..1a8daee 100644
--- a/ttyclock.c
+++ b/ttyclock.c
@@ -426,7 +426,7 @@ main(int argc, char **argv)
           {
           case 'h':
           default:
-               printf("usage : tty-clock [-sctrvih] [-C [0-7]] [-f format]              \n"
+               printf("usage : tty-clock [-sctrvih] [-C [0-7]] [-f format] [-d delay]   \n"
                       "    -s            Show seconds                                   \n"
                       "    -c            Set the clock at the center of the terminal    \n"
                       "    -C [0-7]      Set the clock color                            \n"