diff --git a/radiopadre_client/backends/venv.py b/radiopadre_client/backends/venv.py
index fa42abe..3abe534 100644
--- a/radiopadre_client/backends/venv.py
+++ b/radiopadre_client/backends/venv.py
@@ -172,9 +172,10 @@ def start_session(container_name, selected_ports, userside_ports, notebook_path,
     iglesia.init_helpers(radiopadre_base, verbose=config.VERBOSE > 0,
                          interactive=not config.NBCONVERT, certificate=config.SERVER_PEM)
 
-    # add CARTA UR, if configured
+    # add CARTA URL, if configured
     if config.CARTA_BROWSER and iglesia.CARTA_VERSION:
-        browser_urls.append(iglesia.get_carta_url())
+        if type(browser_urls) is list:
+            browser_urls.append(iglesia.get_carta_url())
 
     ## start jupyter process
     jupyter_path = config.RADIOPADRE_VENV + "/bin/jupyter"