diff --git a/README.md b/README.md
index 589bc19..d2a01fa 100644
--- a/README.md
+++ b/README.md
@@ -165,7 +165,7 @@ bindsym $mod+shift+x exec lock.sh --lock
 # bindsym $mod+shift+x exec lock.sh --lock blur
 
 # Update image cache
-exec --no-startup-id lock.sh -U ~/.wall.png
+exec --no-startup-id lock.sh -u ~/.wall.png
 
 # Set last used image as desktop background, comment out below line if you use different desktop background utility
 exec --no-startup-id lock.sh -w