diff --git a/app/Filament/Resources/EventAchievementResource.php b/app/Filament/Resources/EventAchievementResource.php
index ea3111c4de..2b3fe5a982 100644
--- a/app/Filament/Resources/EventAchievementResource.php
+++ b/app/Filament/Resources/EventAchievementResource.php
@@ -12,6 +12,7 @@
 use App\Models\EventAchievement;
 use App\Models\Game;
 use App\Models\User;
+use Closure;
 use Filament\Forms;
 use Filament\Infolists;
 use Filament\Pages\Page;
@@ -167,6 +168,17 @@ public static function form(Schema $schema): Schema
                                 }
 
                                 return $label;
+                            })
+                            ->rule(function (): Closure {
+                                return function (string $attribute, mixed $value, Closure $fail): void {
+                                    if ($value === null) {
+                                        return;
+                                    }
+
+                                    if (EventAchievement::where('achievement_id', (int) $value)->exists()) {
+                                        $fail('Source achievement cannot be an event achievement.');
+                                    }
+                                };
                             }),
 
                         Forms\Components\DatePicker::make('active_from')