diff --git a/crates/lobby/src/games/db.rs b/crates/lobby/src/games/db.rs
index a309b5d3..41d4ab3d 100644
--- a/crates/lobby/src/games/db.rs
+++ b/crates/lobby/src/games/db.rs
@@ -178,6 +178,7 @@ impl Games {
             AdditionError::OrdinalConflict,
             "UNIQUE constraint failed: players.game, players.ordinal"
         );
+        db_error_message!(result, AdditionError::OrdinalTooLarge, "TOO-LARGE-ORDINAL");
 
         result.map_err(AdditionError::Database)?;
 
@@ -278,6 +279,8 @@ pub(super) enum AdditionError {
     AlreadyInAGame,
     #[error("Another player already joined the game with the same ordinal")]
     OrdinalConflict,
+    #[error("Player ordinal is larger than maximum number of players in the game")]
+    OrdinalTooLarge,
     #[error("The user or the game does not exist")]
     UserOrGameDoesNotExist,
     #[error("A database error encountered")]
diff --git a/crates/lobby/src/games/endpoints.rs b/crates/lobby/src/games/endpoints.rs
index 74ef2679..550ebac3 100644
--- a/crates/lobby/src/games/endpoints.rs
+++ b/crates/lobby/src/games/endpoints.rs
@@ -80,7 +80,11 @@ async fn join(
 ) -> impl Responder {
     let name = path.into_inner();
 
-    // TODO error if ordinal >= max players
+    let ordinal = player_info.ordinal();
+    if ordinal == 0 {
+        warn!("Game joining error: got ordinal equal to 0.");
+        return HttpResponse::BadRequest().json("Ordinals start with 0, got 1.");
+    }
 
     let player = GamePlayer::new(claims.username().to_owned(), player_info.0);
     match games.add_player(&player, name.as_str()).await {
@@ -94,6 +98,11 @@ async fn join(
             HttpResponse::Conflict()
                 .json("Another player has already joined the game under the given ordinal.")
         }
+        Err(AdditionError::OrdinalTooLarge) => {
+            warn!("Game joining error: too large ordinal: {ordinal}");
+            HttpResponse::Conflict()
+                .json("The given ordinal is larger than maximum number of players.")
+        }
         Err(AdditionError::UserOrGameDoesNotExist) => {
             warn!("Game joining error: the game or the user does not exist");
             HttpResponse::NotFound().json("Game not found.")
diff --git a/crates/lobby/src/games/init.sql b/crates/lobby/src/games/init.sql
index 8262b324..ba8cce22 100644
--- a/crates/lobby/src/games/init.sql
+++ b/crates/lobby/src/games/init.sql
@@ -22,3 +22,14 @@ CREATE TABLE IF NOT EXISTS players (
         ON UPDATE CASCADE
         ON DELETE CASCADE
 );
+
+
+CREATE TRIGGER IF NOT EXISTS check_ordinal
+BEFORE INSERT ON players
+FOR EACH ROW
+BEGIN
+    SELECT CASE
+        WHEN (SELECT max_players FROM games WHERE name = NEW.game) IS NOT NULL AND NEW.ordinal > (SELECT max_players FROM games WHERE name = NEW.game)
+        THEN RAISE(FAIL, 'TOO-LARGE-ORDINAL')
+    END;
+END;
diff --git a/crates/lobby_model/src/games.rs b/crates/lobby_model/src/games.rs
index 6b995b35..c388e1bd 100644
--- a/crates/lobby_model/src/games.rs
+++ b/crates/lobby_model/src/games.rs
@@ -17,10 +17,10 @@ pub struct Game {
 }
 
 impl Game {
-    /// Creates a new game with the author having ordinal number of 0 and being
+    /// Creates a new game with the author having ordinal number of 1 and being
     /// the only player.
     pub fn from_author(setup: GameSetup, author: String) -> Self {
-        Self::new(setup, vec![GamePlayer::new(author, GamePlayerInfo::new(0))])
+        Self::new(setup, vec![GamePlayer::new(author, GamePlayerInfo::new(1))])
     }
 
     pub fn new(setup: GameSetup, players: Vec<GamePlayer>) -> Self {
@@ -64,7 +64,11 @@ pub struct GamePlayerInfo {
 }
 
 impl GamePlayerInfo {
+    /// # Panics
+    ///
+    /// Panics if ordinal equal to 0 is used.
     pub fn new(ordinal: u8) -> Self {
+        assert!(ordinal > 0);
         Self { ordinal }
     }
 
diff --git a/docs/src/multiplayer/openapi.yaml b/docs/src/multiplayer/openapi.yaml
index 4225db16..b036b106 100644
--- a/docs/src/multiplayer/openapi.yaml
+++ b/docs/src/multiplayer/openapi.yaml
@@ -170,10 +170,10 @@ paths:
               properties:
                 ordinal:
                   type: integer
-                  minimum: 0
+                  minimum: 1
                   description: >-
                     Each player of the game has a unique number in the range
-                    from 0 to N, where N is the maximum allowed number of
+                    from 1 to N, where N is the maximum allowed number of
                     players in the game. This parameter sets the number for the
                     joining player.
       responses:
@@ -189,7 +189,8 @@ paths:
           description: The game does not exist.
         "409":
           description: >-
-            Another player with the same ordinal has already joined the game.
+            The ordinal is too large or another player with the same ordinal
+            has already joined the game.
 
   /a/games/{name}/leave:
     put: