diff --git a/src/main/java/com/uniovi/controllers/GameController.java b/src/main/java/com/uniovi/controllers/GameController.java
index 3762ac5d..1baa3664 100644
--- a/src/main/java/com/uniovi/controllers/GameController.java
+++ b/src/main/java/com/uniovi/controllers/GameController.java
@@ -74,10 +74,15 @@ public String getMultiplayerGame() {
 
     @GetMapping("/multiplayerGame/{code}")
     public String joinMultiplayerGame(@PathVariable String code, HttpSession session, Principal principal, Model model) {
+        if (!multiplayerSessionService.existsCode(code)) {
+            model.addAttribute("errorKey", "multi.code.invalid");
+            return "game/multiplayerGame";
+        }
+
         Optional<Player> player = playerService.getUserByUsername(principal.getName());
         Player p = player.orElse(null);
         isMultiPlayer=true;
-        if(playerService.changeMultiplayerCode(p.getId(),code)){
+        if (playerService.changeMultiplayerCode(p.getId(),code)) {
             multiplayerSessionService.addToLobby(code,p.getId());
             model.addAttribute("multiplayerGameCode",code);
             session.setAttribute("multiplayerCode",code);
@@ -153,6 +158,7 @@ public List<String> updatePlayerList(@PathVariable String code) {
         Collections.sort(playerNames);
         return playerNames;
     }
+
     @GetMapping("/game/lobby")
     public String createLobby( HttpSession session, Model model) {
         int code = Integer.parseInt((String)session.getAttribute("multiplayerCode"));
diff --git a/src/main/java/com/uniovi/services/MultiplayerSessionService.java b/src/main/java/com/uniovi/services/MultiplayerSessionService.java
index c0932339..7b917458 100644
--- a/src/main/java/com/uniovi/services/MultiplayerSessionService.java
+++ b/src/main/java/com/uniovi/services/MultiplayerSessionService.java
@@ -19,4 +19,6 @@ public interface MultiplayerSessionService {
     void addToLobby(String code, Long id);
 
     void changeScore(String code,Long id,int score);
+
+    boolean existsCode(String code);
 }
diff --git a/src/main/java/com/uniovi/services/impl/MultiplayerSessionImpl.java b/src/main/java/com/uniovi/services/impl/MultiplayerSessionImpl.java
index 0c10044e..4570b8ad 100644
--- a/src/main/java/com/uniovi/services/impl/MultiplayerSessionImpl.java
+++ b/src/main/java/com/uniovi/services/impl/MultiplayerSessionImpl.java
@@ -34,7 +34,7 @@ public Map<Player, Integer> getPlayersWithScores(int multiplayerCode) {
         List<Player> sortedPlayers = playerScores.entrySet().stream()
                 .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
                 .map(Map.Entry::getKey)
-                .collect(Collectors.toList());
+                .toList();
 
         Map<Player, Integer> playersSorted = new HashMap<>();
         for (Player player : sortedPlayers) {
@@ -45,25 +45,38 @@ public Map<Player, Integer> getPlayersWithScores(int multiplayerCode) {
 
     @Override
     public void multiCreate(String code, Long id) {
-        Player p = playerRepository.findById(id).get();
-        multiplayerSessionRepository.save(new MultiplayerSession(code,p));
+        Player p = playerRepository.findById(id).orElse(null);
+
+        if (p != null)
+            multiplayerSessionRepository.save(new MultiplayerSession(code,p));
     }
 
     @Override
     @Transactional
     public void addToLobby(String code, Long id) {
-        Player p = playerRepository.findById(id).get();
-        MultiplayerSession ms=multiplayerSessionRepository.findByMultiplayerCode(code);
-        ms.addPlayer(p);
-        multiplayerSessionRepository.save(ms);
+        Player p = playerRepository.findById(id).orElse(null);
+
+        if (p != null) {
+            MultiplayerSession ms = multiplayerSessionRepository.findByMultiplayerCode(code);
+            ms.addPlayer(p);
+            multiplayerSessionRepository.save(ms);
+        }
     }
 
     @Override
     @Transactional
     public void changeScore(String code, Long id, int score) {
-        Player p = playerRepository.findById(id).get();
-        MultiplayerSession ms=multiplayerSessionRepository.findByMultiplayerCode(code);
-        ms.getPlayerScores().put(p,score);
-        multiplayerSessionRepository.save(ms);
+        Player p = playerRepository.findById(id).orElse(null);
+
+        if (p != null) {
+            MultiplayerSession ms = multiplayerSessionRepository.findByMultiplayerCode(code);
+            ms.getPlayerScores().put(p, score);
+            multiplayerSessionRepository.save(ms);
+        }
+    }
+
+    @Override
+    public boolean existsCode(String code) {
+        return multiplayerSessionRepository.findByMultiplayerCode(code) != null;
     }
 }
diff --git a/src/main/java/com/uniovi/services/impl/PlayerServiceImpl.java b/src/main/java/com/uniovi/services/impl/PlayerServiceImpl.java
index f8cde7ee..c3c7e566 100644
--- a/src/main/java/com/uniovi/services/impl/PlayerServiceImpl.java
+++ b/src/main/java/com/uniovi/services/impl/PlayerServiceImpl.java
@@ -15,17 +15,19 @@
 import org.springframework.stereotype.Service;
 import com.uniovi.entities.Role;
 
+import java.security.SecureRandom;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
+import java.util.Random;
 
 @Service
 public class PlayerServiceImpl implements PlayerService {
     private final PlayerRepository playerRepository;
     private final RoleService roleService;
     private final PasswordEncoder passwordEncoder;
-
-    private MultiplayerSessionService multiplayerSessionService;
+    private final MultiplayerSessionService multiplayerSessionService;
+    private final Random random = new SecureRandom();
 
     public PlayerServiceImpl(PlayerRepository playerRepository, RoleService roleService, MultiplayerSessionService multiplayerSessionService,PasswordEncoder passwordEncoder) {
         this.playerRepository = playerRepository;
@@ -190,7 +192,7 @@ public int createMultiplayerGame(Long id){
             return -1;
 
         Player p = player.get();
-        int code = (int)Math.floor(Math.random()*10000);
+        int code = random.nextInt(10000);
         p.setMultiplayerCode(code);
         playerRepository.save(p);
         return code;
diff --git a/src/main/resources/messages.properties b/src/main/resources/messages.properties
index ea14131d..d8d8fa7f 100644
--- a/src/main/resources/messages.properties
+++ b/src/main/resources/messages.properties
@@ -108,6 +108,7 @@ multi.results =Ver resultados
 multi.finished= Partida finalizada
 multi.points = Puntuaciones
 multi.menu = Ir a la página de inicio
+multi.code.invalid = Código de partida inválido
 # -------------------Statements for the apiHome.html file---------------------
 api.doc.title=Documentación de la API
 api.doc.description=Esta es la documentación de la API de WIQ. Aquí puedes encontrar información sobre los recursos disponibles, los parámetros que aceptan y los ejemplos de uso.
diff --git a/src/main/resources/messages_en.properties b/src/main/resources/messages_en.properties
index 479c891f..be8a7d16 100644
--- a/src/main/resources/messages_en.properties
+++ b/src/main/resources/messages_en.properties
@@ -110,7 +110,7 @@ multi.results = See results
 multi.finished= Finished game
 multi.points = Points
 multi.menu =Go to home page
-
+multi.code.invalid = Invalid game code
 
 # -------------------Statements for the apiHome.html file---------------------
 api.doc.title=API Documentation
diff --git a/src/main/resources/messages_es.properties b/src/main/resources/messages_es.properties
index 3a860636..08bd8b34 100644
--- a/src/main/resources/messages_es.properties
+++ b/src/main/resources/messages_es.properties
@@ -110,7 +110,7 @@ multi.results =Ver resultados
 multi.finished= Partida finalizada
 multi.points = Puntuaciones
 multi.menu = Ir a la página de inicio
-
+multi.code.invalid = Código de partida inválido
 
 # -------------------Statements for the apiHome.html file---------------------
 api.doc.title=Documentación de la API
diff --git a/src/main/resources/messages_fr.properties b/src/main/resources/messages_fr.properties
index 96a377f1..ff7f4cee 100644
--- a/src/main/resources/messages_fr.properties
+++ b/src/main/resources/messages_fr.properties
@@ -103,7 +103,7 @@ multi.results=Voir les résultats
 multi.finished= Jeu terminé
 multi.points = Points
 multi.menu =aller à la page d'accueil
-
+multi.code.invalid = Code invalide
 
 # -------------------Statements for the apiHome.html file---------------------
 api.doc.title=Documentation de l'API
diff --git a/src/main/resources/templates/game/multiplayerGame.html b/src/main/resources/templates/game/multiplayerGame.html
index 6b26fe71..a25a8d44 100644
--- a/src/main/resources/templates/game/multiplayerGame.html
+++ b/src/main/resources/templates/game/multiplayerGame.html
@@ -7,6 +7,7 @@
 <nav th:replace="~{fragments/nav}"></nav>
 
 <div class="container" style="text-align: center">
+    <span class="alert alert-danger" th:if="${errorKey}" th:text="#{${errorKey}}"></span>
     <label id="label-code" class="form-label col-sm-10 text-center mb-3" for="code" th:text="#{multi.label}"></label>
     <div class="form-group col-sm-8 mx-auto">
         <input type="text" class="form-control w-80 mx-auto" id="code" name="code"
diff --git a/src/test/java/com/uniovi/steps/GameStep.java b/src/test/java/com/uniovi/steps/GameStep.java
index ba479c8f..59fdb022 100644
--- a/src/test/java/com/uniovi/steps/GameStep.java
+++ b/src/test/java/com/uniovi/steps/GameStep.java
@@ -8,6 +8,7 @@
 import io.cucumber.java.en.And;
 import io.cucumber.java.en.Then;
 import io.cucumber.java.en.When;
+import org.junit.jupiter.api.Assertions;
 import org.openqa.selenium.By;
 import org.openqa.selenium.WebElement;
 import org.slf4j.Logger;
@@ -18,12 +19,13 @@
 import java.util.List;
 
 public class GameStep extends Wiq_IntegrationTests {
-
     @Autowired
     private InsertSampleDataService dataService;
     @Autowired
     private QuestionGeneratorService questionGeneratorService;
 
+    private String code = "";
+
     private Logger log = LoggerFactory.getLogger(GameStep.class);
 
     @When("I press Play")
@@ -78,4 +80,26 @@ public void iPressStart() {
         List<WebElement> elems = SeleniumUtils.waitLoadElementsBy(driver, "id", "startBtn", 5);
         elems.get(0).click();
     }
+
+    @And("I save the code")
+    public void iSaveACode() {
+        List<WebElement> elems = SeleniumUtils.waitLoadElementsBy(driver, "id", "lobbyCode", 5);
+        Assertions.assertEquals(1, elems.size());
+        code = elems.get(0).getText();
+    }
+
+    @And("I fill in the saved code")
+    public void iFillInTheSavedCode() {
+        List<WebElement> elems = SeleniumUtils.waitLoadElements(driver, By.xpath("//input[contains(@id,'code')]"), 5);
+        elems.get(0).sendKeys(code);
+        elems = SeleniumUtils.waitLoadElementsBy(driver, "id", "joinBtn", 5);
+        elems.get(0).click();
+    }
+
+    @And("I see the multiplayer results")
+    public void iSeeTheMultiplayerResults() {
+        List<WebElement> elems = SeleniumUtils.waitLoadElementsBy(driver, "id", "createBtn", 5);
+        Assertions.assertEquals(1, elems.size());
+        elems.get(0).click();
+    }
 }
diff --git a/src/test/resources/features/MultiplayerGame.feature b/src/test/resources/features/MultiplayerGame.feature
index 0ec53959..c7e93ef1 100644
--- a/src/test/resources/features/MultiplayerGame.feature
+++ b/src/test/resources/features/MultiplayerGame.feature
@@ -8,4 +8,25 @@ Feature: I play a multiplayer game
       When I press Play With Friends
       And I create a code
       And I press start
-      Then I should start playing until I see message "multi.finished"
\ No newline at end of file
+      Then I should start playing until I see message "multi.finished"
+
+  Scenario: I start a multiplayer game
+    Given I am not registered or logged in
+    And I am on the register page
+    When I fill in the form with valid data username: "userGame" email: "userGame@gmail.com" password: "password" password_confirmation: "password"
+    And I press the register button
+    And I go to the home page
+    When I press Play With Friends
+    And I create a code
+    And I save the code
+    Then I logout
+    Given I am not registered or logged in
+    And I am on the register page
+    When I fill in the form with valid data username: "userGame2" email: "userGame2@gmail.com" password: "password" password_confirmation: "password"
+    And I press the register button
+    And I go to the home page
+    And I press Play With Friends
+    And I fill in the saved code
+    And I press start
+    Then I should start playing until I see message "multi.finished"
+    And I see the multiplayer results
\ No newline at end of file