diff --git a/config/settings/_base.py b/config/settings/_base.py
index bd833762..b15d770a 100644
--- a/config/settings/_base.py
+++ b/config/settings/_base.py
@@ -37,8 +37,9 @@
 # Get the IP to use for Django Debug Toolbar when developing with docker
 if env.bool("USE_DOCKER", default=False) is True:
     ip = socket.gethostbyname(socket.gethostname())
-    if ip is not None:
-        INTERNAL_IPS += [ip[:-1] + "1"]
+    if INTERNAL_IPS is None:  # Ensure INTERNAL_IPS is a list
+        INTERNAL_IPS = []
+    INTERNAL_IPS += [ip[:-1] + "1"]
 
 # Application definition