diff --git a/setup/webmail.sh b/setup/webmail.sh
index fbb489f4..37b00b41 100755
--- a/setup/webmail.sh
+++ b/setup/webmail.sh
@@ -36,7 +36,7 @@ if [ ! -d /usr/local/lib/roundcubemail ]; then
 fi
 
 # Generate a safe 24-character secret key of safe characters.
-SECRET_KEY=$(dd if=/dev/random bs=20 count=1 2>/dev/null | base64 | fold -w 24 | head -n 1)
+SECRET_KEY=$(dd if=/dev/random bs=1 count=18 2>/dev/null | base64 | fold -w 24 | head -n 1)
 
 # Create a configuration file.
 #