diff --git a/libwallet/src/api_impl/foreign.rs b/libwallet/src/api_impl/foreign.rs
index bf9308c..e8a8e8c 100644
--- a/libwallet/src/api_impl/foreign.rs
+++ b/libwallet/src/api_impl/foreign.rs
@@ -276,7 +276,9 @@ where
 	C: NodeClient + 'a,
 	K: Keychain + 'a,
 {
-	let net_change = args.net_change.unwrap();
+	let net_change = args.net_change.ok_or_else(|| {
+		Error::GenericError("Contract requires a net change (--send or --receive)".to_string())
+	})?;
 	if net_change <= 0 {
 		return Err(Error::GenericError(
 			"Can't sign a non-receiving contract from a foreign API.".to_string(),