diff --git a/python/obitools3/commands/cat.pyx b/python/obitools3/commands/cat.pyx
index a70839f..bfb63b2 100755
--- a/python/obitools3/commands/cat.pyx
+++ b/python/obitools3/commands/cat.pyx
@@ -97,7 +97,7 @@ def run(config):
             Column.new_column(o_view, REVERSE_QUALITY_COLUMN, OBI_QUAL, associated_column_name=REVERSE_SEQUENCE_COLUMN, associated_column_version=o_view[REVERSE_SEQUENCE_COLUMN].version)
         
     # Initialize multiple elements columns
-    if type(output_0)==BufferedWriter: 
+    if type(output_0)!=BufferedWriter: 
         dict_cols = {}
         for v_uri in config["cat"]["views_to_cat"]:
             v = open_uri(v_uri)[1]