diff --git a/setup/start.sh b/setup/start.sh
index 7d26466a..7cdbec17 100755
--- a/setup/start.sh
+++ b/setup/start.sh
@@ -92,7 +92,8 @@ if [ -z "$PRIMARY_HOSTNAME" ]; then
 
 		# Take the part after the @-sign as the user's domain name, and add
 		# 'box.' to the beginning to create a default hostname for this machine.
-		DEFAULT_PRIMARY_HOSTNAME=box.$(echo $EMAIL_ADDR | sed 's/.*@//')
+		# If there is already a 'box.' in the EMAIL_ADDR, strip it from the string.
+		DEFAULT_PRIMARY_HOSTNAME=box.$(echo $EMAIL_ADDR | sed -e 's/.*@//' -e 's/^box\.//')
 	fi
 
 	echo