diff --git a/module.nix b/module.nix
index 9ec4ff6..10f26a1 100644
--- a/module.nix
+++ b/module.nix
@@ -63,6 +63,12 @@ in
       description = "Maximum length for messages. 0 for unlimited.";
     };
 
+    maxWebsiteLength = mkOption {
+      type = types.int;
+      default = 100;
+      description = "Maximum length for website URLs. 0 for unlimited.";
+    };
+
     user = mkOption {
       type = types.str;
       default = "guestbook";
@@ -101,6 +107,7 @@ in
           BOOK_HONEYPOT = if cfg.honeypot then "true" else "false";
           BOOK_MAX_NAME_LENGTH = toString cfg.maxNameLength;
           BOOK_MAX_MESSAGE_LENGTH = toString cfg.maxMessageLength;
+          BOOK_MAX_WEBSITE_LENGTH = toString cfg.maxWebsiteLength;
         };
         serviceConfig = {
           Type = "simple";
diff --git a/src/config.rs b/src/config.rs
index cccf1d4..64f67c7 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -12,6 +12,7 @@ pub struct Config {
     pub honeypot: bool,
     pub max_name_length: usize,
     pub max_message_length: usize,
+    pub max_website_length: usize,
 }
 
 impl Config {
@@ -47,6 +48,10 @@ impl Config {
                 .unwrap_or_else(|_| "1000".into())
                 .parse()
                 .map_err(|_| "BOOK_MAX_MESSAGE_LENGTH must be a number")?,
+            max_website_length: env::var("BOOK_MAX_WEBSITE_LENGTH")
+                .unwrap_or_else(|_| "100".into())
+                .parse()
+                .map_err(|_| "BOOK_MAX_WEBSITE_LENGTH must be a number")?,
         })
     }
 }
@@ -54,9 +59,13 @@ impl Config {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::sync::Mutex;
+
+    static ENV_LOCK: Mutex<()> = Mutex::new(());
 
     #[test]
     fn test_from_env() {
+        let _lock = ENV_LOCK.lock().unwrap();
         env::set_var("BOOK_PORT", "9999");
         env::set_var("BOOK_DATA_DIR", "/tmp/gb");
         env::set_var("BOOK_SITE_TITLE", "test.rs");
@@ -83,6 +92,7 @@ mod tests {
 
     #[test]
     fn test_defaults() {
+        let _lock = ENV_LOCK.lock().unwrap();
         env::set_var("BOOK_SITE_URL", "https://test.rs");
         env::set_var("BOOK_TELEGRAM_BOT_TOKEN", "123:ABC");
         env::set_var("BOOK_TELEGRAM_CHAT_ID", "12345");
@@ -99,6 +109,7 @@ mod tests {
 
     #[test]
     fn test_missing_required() {
+        let _lock = ENV_LOCK.lock().unwrap();
         env::remove_var("BOOK_SITE_URL");
         env::remove_var("BOOK_TELEGRAM_BOT_TOKEN");
         env::remove_var("BOOK_TELEGRAM_CHAT_ID");
diff --git a/src/web.rs b/src/web.rs
index 17f9761..7a53b51 100644
--- a/src/web.rs
+++ b/src/web.rs
@@ -69,8 +69,9 @@ async fn submit(
     if max_name > 0 && name.len() > max_name {
         return Html(format!("Name is too long (max {max_name} chars)."));
     }
-    if website.len() > 100 {
-        return Html("Website is too long (max 100 chars).".to_string());
+    let max_web = state.config.max_website_length;
+    if max_web > 0 && website.len() > max_web {
+        return Html(format!("Website is too long (max {max_web} chars)."));
     }
     let max_msg = state.config.max_message_length;
     if max_msg > 0 && message.len() > max_msg {