diff --git a/src/allmydata/client.py b/src/allmydata/client.py
index e03e9ca47..d9c77b7e3 100644
--- a/src/allmydata/client.py
+++ b/src/allmydata/client.py
@@ -256,6 +256,10 @@ class Client(node.Node, pollmixin.PollMixin):
 
         # read furl from tahoe.cfg
         tahoe_cfg_introducer_furl = self.get_config("client", "introducer.furl", None)
+        if tahoe_cfg_introducer_furl == "None":
+            raise ValueError("tahoe.cfg has invalid 'introducer.furl = None':"
+                             " to disable it, use 'introducer.furl ='"
+                             " or omit the key entirely")
         if tahoe_cfg_introducer_furl:
             introducers[u'default'] = {'furl':tahoe_cfg_introducer_furl}
 
diff --git a/src/allmydata/scripts/create_node.py b/src/allmydata/scripts/create_node.py
index 41002deb7..5f1166df3 100644
--- a/src/allmydata/scripts/create_node.py
+++ b/src/allmydata/scripts/create_node.py
@@ -279,7 +279,8 @@ def write_node_config(c, config):
 def write_client_config(c, config):
     c.write("[client]\n")
     c.write("# Which services should this client connect to?\n")
-    c.write("introducer.furl = %s\n" % config.get("introducer", ""))
+    introducer = config.get("introducer", None) or ""
+    c.write("introducer.furl = %s\n" % introducer)
     c.write("helper.furl =\n")
     c.write("#stats_gatherer.furl =\n")
     c.write("\n")