--- a/tincan.py	Fri May 31 08:23:37 2019 -0700
+++ b/tincan.py	Fri May 31 08:45:39 2019 -0700
@@ -892,9 +892,11 @@
     if fsroot is None:
         fsroot = os.getcwd()
     launcher = _Launcher(fsroot, urlroot, multithread)
-    for i in [ "logger", "encoding", "static" ]:
-        if i in kwargs:
-            setattr(launcher, i, kwargs[i])
+    allowed = set(["logger", "encoding", "static"])
+    for k, v in kwargs.items():
+        if k not in allowed:
+            raise TypeError("launch() got an unexpected keyword argument {0!r}".format(k))
+        setattr(launcher, k, v)
     launcher.launch()
     return launcher.app, launcher.errors