diff --git a/biggus/__init__.py b/biggus/__init__.py
index d3fdd43..3dd5659 100644
--- a/biggus/__init__.py
+++ b/biggus/__init__.py
@@ -82,6 +82,8 @@ def ndarrays(arrays):
         """
         return [array.ndarray() for array in arrays]
 
+    __hash__ = None
+
     def __repr__(self):
         return '<{} shape={} dtype={!r}>'.format(type(self).__name__,
                                                  self.shape, self.dtype)
diff --git a/biggus/tests/unit/__init__.py b/biggus/tests/unit/__init__.py
new file mode 100644
index 0000000..de8dd0a
--- /dev/null
+++ b/biggus/tests/unit/__init__.py
@@ -0,0 +1,17 @@
+# (C) British Crown Copyright 2014, Met Office
+#
+# This file is part of Biggus.
+#
+# Biggus is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Biggus 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 Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with Biggus. If not, see <http://www.gnu.org/licenses/>.
+"""Unit tests for biggus."""
diff --git a/biggus/tests/unit/test_Array.py b/biggus/tests/unit/test_Array.py
new file mode 100644
index 0000000..3119ff9
--- /dev/null
+++ b/biggus/tests/unit/test_Array.py
@@ -0,0 +1,50 @@
+# (C) British Crown Copyright 2014, Met Office
+#
+# This file is part of Biggus.
+#
+# Biggus is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Biggus 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 Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with Biggus. If not, see <http://www.gnu.org/licenses/>.
+"""Unit tests for `biggus.Array`."""
+
+import unittest
+
+from biggus import Array
+
+
+class Test___hash__(unittest.TestCase):
+    def test_unhashable(self):
+        class FakeArray(Array):
+            @property
+            def dtype(self):
+                pass
+
+            @property
+            def shape(self):
+                pass
+
+            def __getitem__(self, keys):
+                pass
+
+            def ndarray(self, keys):
+                pass
+
+            def masked_array(self, keys):
+                pass
+
+        array = FakeArray()
+        with self.assertRaises(TypeError):
+            hash(array)
+
+
+if __name__ == '__main__':
+    unittest.main()