diff --git a/diffsims/sims/__init__.py b/diffsims/sims/__init__.py
new file mode 100644
index 00000000..6f9152dd
--- /dev/null
+++ b/diffsims/sims/__init__.py
@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017-2019 The diffsims developers
+#
+# This file is part of diffsims.
+#
+# diffsims is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# diffsims is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with diffsims.  If not, see <http://www.gnu.org/licenses/>.