diff --git a/src/config.rs b/src/config.rs
index c6df5e9..713e4ca 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -5,6 +5,7 @@ use std::fs;
 use std::path::PathBuf;
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(default)]
 pub struct ServerConfig {
     pub port: u16,
     pub bind: String,
@@ -95,6 +96,7 @@ impl Default for ServerConfig {
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(default)]
 pub struct ClientConfig {
     pub update_repo: Option<String>,
     pub update_port: Option<u16>,
@@ -330,3 +332,63 @@ pub fn expand_tilde(path: &str) -> PathBuf {
     }
     PathBuf::from(path)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{ClientConfig, ServerConfig};
+
+    #[test]
+    fn old_client_configs_fill_new_fields_from_defaults() {
+        let raw = r#"
+server = "palav"
+dosh_port = 50000
+"#;
+
+        let config: ClientConfig = toml::from_str(raw).expect("parse old client config");
+
+        assert_eq!(config.server, "palav");
+        assert!(config.predict);
+        assert_eq!(config.predict_mode, "experimental");
+        assert_eq!(config.auth_preference, "native,ssh");
+        assert_eq!(config.native_auth_timeout_ms, 700);
+        assert_eq!(config.known_hosts, "~/.config/dosh/known_hosts");
+        assert_eq!(config.identity_files, vec!["~/.ssh/id_ed25519"]);
+        assert!(config.use_ssh_agent);
+        assert!(!config.forward_agent);
+        assert!(config.disconnect_status);
+        assert_eq!(config.escape_key, "^]");
+        assert!(config.send_env.iter().any(|value| value == "TERM"));
+    }
+
+    #[test]
+    fn old_server_configs_fill_new_fields_from_defaults() {
+        let raw = r#"
+port = 50000
+"#;
+
+        let config: ServerConfig = toml::from_str(raw).expect("parse old server config");
+
+        assert_eq!(config.port, 50000);
+        assert_eq!(config.bind, "0.0.0.0");
+        assert_eq!(config.client_timeout_secs, 2_592_000);
+        assert_eq!(config.output_frame_interval_ms, 16);
+        assert!(config.native_auth);
+        assert_eq!(config.host_key, "~/.config/dosh/host_key");
+        assert!(
+            config
+                .authorized_keys
+                .iter()
+                .any(|path| path == "~/.ssh/authorized_keys")
+        );
+        assert_eq!(config.native_auth_rate_limit_per_minute, 30);
+        assert_eq!(config.rekey_after_packets, 100_000);
+        assert_eq!(config.rekey_after_secs, 3600);
+        assert!(config.allow_tcp_forwarding);
+        assert!(!config.allow_remote_forwarding);
+        assert!(!config.allow_agent_forwarding);
+        assert!(config.allow_file_transfer);
+        assert!(config.allow_exec_command);
+        assert!(config.persist_sessions);
+        assert!(config.accept_env.iter().any(|value| value == "TERM"));
+    }
+}