diff --git a/spynnaker/pyNN/models/neural_projections/connectors/one_to_one_offset_connector.py b/spynnaker/pyNN/models/neural_projections/connectors/one_to_one_offset_connector.py
index 628b57ab96..43e5dc61d0 100644
--- a/spynnaker/pyNN/models/neural_projections/connectors/one_to_one_offset_connector.py
+++ b/spynnaker/pyNN/models/neural_projections/connectors/one_to_one_offset_connector.py
@@ -200,6 +200,9 @@ def gen_connector_params(
         n_values = self.__n_neurons_per_group
         if n_values is None:
             n_values = synapse_info.n_pre_neurons
+        assert self.__offset >= 0
+        assert self.__wrap >= 0
+        assert n_values >= 0
         return numpy.array([self.__offset, int(self.__wrap), n_values],
                            dtype=uint32)