diff --git a/parse_args b/parse_args
index 37c5f679..3244e31e 100755
--- a/parse_args
+++ b/parse_args
@@ -187,7 +187,7 @@ def main():
         try:
             with open('/etc/yunohost/installed') as f: pass
         except IOError:
-            if sys.argv[1] != 'tools' or sys.argv[2] != 'postinstall':
+            if len(sys.argv) < 3 or sys.argv[1] != 'tools' or sys.argv[2] != 'postinstall':
                 raise YunoHostError(17, _("YunoHost is not correctly installed, please execute 'yunohost tools postinstall'"))
 
         args = parse_dict(action_map)