diff --git a/tests/unit_tests/test_mesh.py b/tests/unit_tests/test_mesh.py
new file mode 100644
index 000000000..08dd65e33
--- /dev/null
+++ b/tests/unit_tests/test_mesh.py
@@ -0,0 +1,9 @@
+import openmc
+import pytest
+
+def test_raises_error_when_flat():
+    with pytest.raises(ValueError):
+        mesh = openmc.RegularMesh()
+        mesh.dimension = [50, 50, 1]
+        mesh.lower_left = [-25, -25, 0]
+        mesh.upper_right = [25, 25, 0]
\ No newline at end of file