diff --git a/unittests/test_add_property.py b/unittests/test_add_property.py
index 3d7f53dbd3bba05f771c623a3b563bd981f7c431..874314ee62d5471a9e859d8c4dc44c4e4a6532c7 100644
--- a/unittests/test_add_property.py
+++ b/unittests/test_add_property.py
@@ -199,14 +199,16 @@ def test_property_parameter_with_entity_and_datatype():
     assert concrete_property.value is None
     assert concrete_property.datatype == db.INTEGER
 
-    concrete_property.datatype = None
+    concrete_property.datatype = db.DOUBLE
     concrete_property.value = 3.14
 
     with raises(ValueError):
         # cannot parse 3.14 to integer
         concrete_property.datatype = db.INTEGER
-    concrete_property.datatype = None
-    concrete_property.value = 3.14
+
+    # nothing should've changed after the ValueError
+    assert concrete_property.datatype == db.DOUBLE
+    assert concrete_property.value == 3.14
 
 
 def test_kw_name_and_value():