diff --git a/pywr-schema/src/model.rs b/pywr-schema/src/model.rs
index 84fa6b0c..c2a17556 100644
--- a/pywr-schema/src/model.rs
+++ b/pywr-schema/src/model.rs
@@ -879,7 +879,7 @@ impl PywrMultiNetworkModel {
         let mut model = pywr_core::models::MultiNetworkModel::new(domain);
 
         for (name, network) in networks {
-            model.add_network(&name, network);
+            model.add_network(&name, network)?;
         }
 
         for (from_network_idx, from_metric, to_network_idx, initial_value) in inter_network_transfers {