diff --git a/README.md b/README.md
index 0b2b04a..ebf31f0 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,7 @@ Usage: hesinde-sync [OPTIONS]
 Options:
   -a, --address <ADDRESS>              Address to listen on [env: ADDRESS=] [default: localhost:3030]
   -d, --db-connection <DB_CONNECTION>  From which file to read the database connection string ("-" for stdin) [env: DB_CONNECTION=] [default: -]
+  -a, --allow-registering              Whether new users can register [env: ALLOW_REGISTERING=]
   -h, --help                           Print help
   -V, --version                        Print version
 ```
diff --git a/app/src/api.rs b/app/src/api.rs
index bce8c0a..290308c 100644
--- a/app/src/api.rs
+++ b/app/src/api.rs
@@ -78,6 +78,8 @@ pub struct Api;
 impl Api {
     /// Register a new user.
     ///
+    /// If registration is disabled return early.
+    ///
     /// If a user of that id already exist, return a conflict.
     #[oai(path = "/users/create", method = "post")]
     async fn register(
@@ -85,7 +87,14 @@ impl Api {
         req: Json<RegisterRequest>,
         state: Data<&Arc<AppState>>,
     ) -> Result<payload::Response<payload::Json<UserCreated>>> {
-        let db = &state.0.db;
+        if !state.config.allow_registration {
+            return Err(Error::from_string(
+                "Registration is disabled.",
+                StatusCode::UNAUTHORIZED,
+            ));
+        }
+
+        let db = &state.db;
         if db.get_user(&req.username).await?.is_some() {
             Err(Error::from_status(StatusCode::CONFLICT))
         } else {
diff --git a/app/src/cli.rs b/app/src/cli.rs
index f32c98e..184d485 100644
--- a/app/src/cli.rs
+++ b/app/src/cli.rs
@@ -13,4 +13,8 @@ pub struct Config {
     /// From which file to read the database connection string ("-" for stdin)
     #[arg(short, long, env, default_value = "-")]
     pub db_connection: String,
+
+    /// Whether new users can register.
+    #[arg(short = 'r', long, env, default_value = "false")]
+    pub allow_registration: bool,
 }
diff --git a/app/src/main.rs b/app/src/main.rs
index 51516aa..f4fd279 100644
--- a/app/src/main.rs
+++ b/app/src/main.rs
@@ -15,6 +15,7 @@ async fn main() -> Result<()> {
     tracing_subscriber::fmt::init();
 
     let args = Config::parse();
+    println!("{}", args.allow_registration);
     let db_url = read_db_url(&args.db_connection)?;
 
     hesinde_sync::run(&args, &db_url).await