diff --git a/iobber/corpio.py b/iobber/corpio.py
index 7481414a8d51202dddbe19bb6154384d71929cf9..84095cd3be7d2bee2ffde0ccc1da8e9a9fe56351 100644
--- a/iobber/corpio.py
+++ b/iobber/corpio.py
@@ -55,8 +55,9 @@ def get_reader(in_path, tagset, input_format, read_disamb_only):
 	"""Creates a reader using the options. If in_path evaluates to False,
 	will create a stdin reader. Set read_disamb_only to force reading only
 	'disamb' lexemes/interpretations."""
+	fixd_format = input_format
 	if read_disamb_only:
-		fixd_format = input_format + ',disamb_only'
+		fixd_format += ',disamb_only'
 	# force casting sentences as AnnotatedSentences
 	# required to get XCES input right
 	fixd_format += ',ann'