diff --git a/app/Http/Controllers/Api/V1/TimeEntryController.php b/app/Http/Controllers/Api/V1/TimeEntryController.php
index 9c77b2c4..5c44ee50 100644
--- a/app/Http/Controllers/Api/V1/TimeEntryController.php
+++ b/app/Http/Controllers/Api/V1/TimeEntryController.php
@@ -51,6 +51,7 @@ use Illuminate\Support\Carbon;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Facades\Auth;
 use Illuminate\Support\Facades\Blade;
+use Illuminate\Support\Facades\Cache;
 use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Log;
 use Illuminate\Support\Facades\Storage;
@@ -613,6 +614,22 @@ class TimeEntryController extends Controller
             $this->checkPermission($organization, 'time-entries:create:all');
         }
 
+        // Lock the creation of running time entries per user, so that concurrent requests can not create more than one running time entry
+        $lock = $request->input('end') === null ? Cache::lock('time-entries:running:'.$member->user_id, 10) : null;
+        $lock?->block(5);
+
+        try {
+            return $this->storeTimeEntry($organization, $member, $request);
+        } finally {
+            $lock?->release();
+        }
+    }
+
+    /**
+     * @throws TimeEntryStillRunningApiException
+     */
+    private function storeTimeEntry(Organization $organization, Member $member, TimeEntryStoreRequest $request): JsonResource
+    {
         if ($request->input('end') === null && TimeEntry::query()->whereBelongsTo($member, 'member')->where('end', null)->exists()) {
             throw new TimeEntryStillRunningApiException;
         }
diff --git a/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php b/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
index 733693cb..8d9b349d 100644
--- a/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
+++ b/tests/Unit/Endpoint/Api/V1/TimeEntryEndpointTest.php
@@ -24,7 +24,9 @@ use App\Models\Task;
 use App\Models\TimeEntry;
 use App\Models\User;
 use App\Service\TimeEntryFilter;
+use Illuminate\Contracts\Cache\LockTimeoutException;
 use Illuminate\Support\Carbon;
+use Illuminate\Support\Facades\Cache;
 use Illuminate\Support\Facades\Config;
 use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Log;
@@ -2444,6 +2446,52 @@ class TimeEntryEndpointTest extends ApiEndpointTestAbstract
         $response->assertJsonPath('error', true);
     }
 
+    public function test_store_endpoint_releases_running_time_entry_lock_after_request(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:create:own',
+        ]);
+        Passport::actingAs($data->user);
+
+        // Act
+        $response = $this->postJson(route('api.v1.time-entries.store', [$data->organization->getKey()]), [
+            'billable' => true,
+            'start' => Carbon::now()->toIso8601ZuluString(),
+            'end' => null,
+            'member_id' => $data->member->getKey(),
+        ]);
+
+        // Assert
+        $response->assertStatus(201);
+        $this->assertTrue(Cache::lock('time-entries:running:'.$data->user->getKey(), 10)->get());
+    }
+
+    public function test_store_endpoint_waits_for_running_time_entry_lock_and_fails_if_it_is_not_released(): void
+    {
+        // Arrange
+        $data = $this->createUserWithPermission([
+            'time-entries:create:own',
+        ]);
+        Cache::lock('time-entries:running:'.$data->user->getKey(), 10)->get();
+        $this->withoutExceptionHandling();
+        Passport::actingAs($data->user);
+
+        // Act
+        try {
+            $this->postJson(route('api.v1.time-entries.store', [$data->organization->getKey()]), [
+                'billable' => true,
+                'start' => Carbon::now()->toIso8601ZuluString(),
+                'end' => null,
+                'member_id' => $data->member->getKey(),
+            ]);
+            $this->fail('Expected LockTimeoutException');
+        } catch (LockTimeoutException) {
+            // Assert
+            $this->assertSame(0, TimeEntry::query()->count());
+        }
+    }
+
     public function test_store_endpoint_validation_fails_if_task_id_does_not_belong_to_project_id(): void
     {
         // Arrange