diff --git a/setup/questions.sh b/setup/questions.sh
index 3f951706..580a9c8f 100644
--- a/setup/questions.sh
+++ b/setup/questions.sh
@@ -95,7 +95,7 @@ if [ -z "${DAV_HOSTNAME:-}" ]; then
 fi
 
 if [ $DAV_HOSTNAME == $PRIMARY_HOSTNAME ]; then
-    if [ -z "${RC_DOCK}"]; then
+    if [ -z "${RC_DOCK:-}"]; then
         RC_DOCK=n
         input_box "Run Roundcube Webmail in Docker" \ "By default Mail-in-a-Box installs Roundcube onto the host. \
         \n\nDo you want to run Roundcube Webmail in a Docker container instead?" \