diff --git a/src/lib.rs b/src/lib.rs
index 09d8ab0..be42ee8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,12 +29,13 @@ async fn read_req(sock: &mut TcpStream) -> Result<bool, Box<dyn Error + Send + S
     Ok(&buf[..REQ_METHOD.len()] == REQ_METHOD)
 }
 
-pub async fn serve(port: Option<i32>, tz: Option<String>) -> Result<(), Box<dyn Error>> {
-    let addr = format!("127.0.0.1:{}", port.unwrap_or(PORT));
-    let listen = TcpListener::bind(&addr).await?;
-
+pub async fn serve(port: Option<String>, tz: Option<String>) -> Result<(), Box<dyn Error>> {
+    let port = port.and_then(|s| s.parse::<i32>().ok()).unwrap_or(PORT);
     let tz = tz.and_then(|s| s.parse::<Tz>().ok()).unwrap_or(CET);
 
+    let addr = format!("127.0.0.1:{}", port);
+    let listen = TcpListener::bind(&addr).await?;
+
     loop {
         let (mut sock, addr) = listen.accept().await?;
 
diff --git a/src/main.rs b/src/main.rs
index d125171..80493b6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,11 +3,5 @@ use std::error::Error;
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
-    swabd::serve(
-        env::var("SWABD_PORT")
-            .map(|port| port.parse::<i32>().unwrap())
-            .ok(),
-        env::var("SWABD_TZ").ok(),
-    )
-    .await
+    swabd::serve(env::var("SWABD_PORT").ok(), env::var("SWABD_TZ").ok()).await
 }