diff --git a/pyotlss.py b/pyotlss.py
index 14969639d..0850e1699 100755
--- a/pyotlss.py
+++ b/pyotlss.py
@@ -1174,6 +1174,10 @@ layout_features_all = unique_sorted (sum (layout_features_dict.values (), []))
 class Subsetter:
 
 	class Options:
+
+		class UnknownOptionError (Exception):
+			pass
+
 		drop_tables = drop_tables_default
 		no_subset_tables = no_subset_tables_default
 		hinting_tables = hinting_tables_default
@@ -1195,7 +1199,7 @@ class Subsetter:
 		def set (self, **kwargs):
 			for k,v in kwargs.items ():
 				if not hasattr (self, k):
-					raise Exception ("Unknown option '%s'" % k)
+					raise self.UnknownOptionError ("Unknown option '%s'" % k)
 				setattr (self, k, v)
 
 		def parse_opts (self, argv, ignore_unknown=False):
@@ -1224,7 +1228,7 @@ class Subsetter:
 						ret.append (orig_a)
 						continue
 					else:
-						raise Exception ("Unknown option '%s'" % a)
+						raise self.UnknownOptionError ("Unknown option '%s'" % a)
 
 				ov = getattr (self, k)
 				if isinstance (ov, bool):