diff --git a/Lib/fontTools/ttLib/tables/otBase.py b/Lib/fontTools/ttLib/tables/otBase.py
index 0ee5141..e6fd0ab 100644
--- a/Lib/fontTools/ttLib/tables/otBase.py
+++ b/Lib/fontTools/ttLib/tables/otBase.py
@@ -608,12 +608,14 @@
 				name = conv.name
 				writer.writeCountReference(table, name)
 				counts.append(name)
-				def storeValue(value):
-					if table[name] is None:
-						table[name] = value
-					else:
-						assert table[name] == value, (table[name], value)
-				countVars[name] = storeValue
+				def storeValueFactory(table, name):
+					def storeValue(value):
+						if table[name] is None:
+							table[name] = value
+						else:
+							assert table[name] == value, (table[name], value)
+					return storeValue
+				countVars[name] = storeValueFactory(table, name)
 			else:
 				conv.write(writer, font, countVars, value)