diff --git a/tests/Feature/VolunteerTimeEntryStoreTest.php b/tests/Feature/VolunteerTimeEntryStoreTest.php
new file mode 100644
index 00000000..bc52b117
--- /dev/null
+++ b/tests/Feature/VolunteerTimeEntryStoreTest.php
@@ -0,0 +1,59 @@
+<?php
+
+use App\Models\Department;
+use App\Models\Event;
+use App\Models\Role;
+use App\Models\TimeEntry;
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+it('rejects creating a second ongoing time entry for the same user and event', function () {
+	$manager = User::factory()->create(['role' => Role::Admin]);
+	$volunteer = User::factory()->create();
+	$event = Event::factory()->create();
+	$department = Department::factory()->create(['event_id' => $event->id]);
+
+	$this->actingAs($manager);
+
+	// Mirrors the real clock-in UI, which always sends an explicit 'start' and omits 'stop'.
+	$this->putJson(route('volunteer.time.store', [$event, $volunteer]), [
+		'department_id' => $department->id,
+		'start' => now()->subSecond()->toISOString(),
+	])->assertOk();
+
+	expect(TimeEntry::where('user_id', $volunteer->id)->whereNull('stop')->count())->toBe(1);
+
+	$this->putJson(route('volunteer.time.store', [$event, $volunteer]), [
+		'department_id' => $department->id,
+		'start' => now()->subSecond()->toISOString(),
+	])
+		->assertStatus(409)
+		->assertJson(['error' => 'User already has an ongoing time entry.']);
+
+	expect(TimeEntry::where('user_id', $volunteer->id)->whereNull('stop')->count())->toBe(1);
+});
+
+it('allows creating a time entry with an explicit stop while another is ongoing', function () {
+	$manager = User::factory()->create(['role' => Role::Admin]);
+	$volunteer = User::factory()->create();
+	$event = Event::factory()->create();
+	$department = Department::factory()->create(['event_id' => $event->id]);
+
+	$this->actingAs($manager);
+
+	$this->putJson(route('volunteer.time.store', [$event, $volunteer]), [
+		'department_id' => $department->id,
+		'start' => now()->subSecond()->toISOString(),
+	])->assertOk();
+
+	$this->putJson(route('volunteer.time.store', [$event, $volunteer]), [
+		'department_id' => $department->id,
+		'start' => now()->subHour()->toISOString(),
+		'stop' => now()->toISOString(),
+	])->assertOk();
+
+	expect(TimeEntry::where('user_id', $volunteer->id)->count())->toBe(2);
+	expect(TimeEntry::where('user_id', $volunteer->id)->whereNull('stop')->count())->toBe(1);
+});
\ No newline at end of file