diff --git a/openvidu-server/docker/openvidu-coturn/detect-external-ip.sh b/openvidu-server/docker/openvidu-coturn/detect-external-ip.sh
index fccbeae7..7fd6ad1e 100644
--- a/openvidu-server/docker/openvidu-coturn/detect-external-ip.sh
+++ b/openvidu-server/docker/openvidu-coturn/detect-external-ip.sh
@@ -54,7 +54,7 @@ fi
 
 # Shortcut to use internal IP as external IP: COTURN_INTERNAL_RELAY
 # ==========================
-if [ -n "${COTURN_INTERNAL_RELAY}" ] && [ "${COTURN_INTERNAL_RELAY}" = "true" ]; then
+if [ -n "${COTURN_INTERNAL_RELAY:-}" ] && [ "${COTURN_INTERNAL_RELAY:-}" = "true" ]; then
     discover-internal-ip.sh
     exit 0
 fi