diff --git a/pycallgraph/output/graphviz.py b/pycallgraph/output/graphviz.py
index 6f100496..203c0978 100644
--- a/pycallgraph/output/graphviz.py
+++ b/pycallgraph/output/graphviz.py
@@ -45,6 +45,7 @@ def add_arguments(cls, subparsers, parent_parser, usage):
 
         subparser.add_argument(
             '-f', '--output-format', type=str, default=defaults.output_type,
+            dest='output_type',
             help='Image format to produce, e.g. png, ps, dot, etc. '
             'See http://www.graphviz.org/doc/info/output.html for more.',
         )