diff --git a/app/Models/Device.php b/app/Models/Device.php
index 2eeb25b..3583f48 100644
--- a/app/Models/Device.php
+++ b/app/Models/Device.php
@@ -20,6 +20,14 @@ class Device extends Model
 
     protected $guarded = ['id'];
 
+    /**
+     * Set the MAC address attribute, normalizing to uppercase.
+     */
+    public function setMacAddressAttribute(?string $value): void
+    {
+        $this->attributes['mac_address'] = $value ? mb_strtoupper($value) : null;
+    }
+
     protected $casts = [
         'battery_notification_sent' => 'boolean',
         'proxy_cloud' => 'boolean',
diff --git a/routes/api.php b/routes/api.php
index 9721a0f..d1dbcac 100644
--- a/routes/api.php
+++ b/routes/api.php
@@ -18,7 +18,7 @@ use Illuminate\Support\Str;
 Route::get('/display', function (Request $request) {
     $mac_address = $request->header('id');
     $access_token = $request->header('access-token');
-    $device = Device::where('mac_address', $mac_address)
+    $device = Device::where('mac_address', mb_strtoupper($mac_address ?? ''))
         ->where('api_key', $access_token)
         ->first();
 
@@ -29,7 +29,7 @@ Route::get('/display', function (Request $request) {
         if ($auto_assign_user) {
             // Create a new device and assign it to this user
             $device = Device::create([
-                'mac_address' => $mac_address,
+                'mac_address' => mb_strtoupper($mac_address ?? ''),
                 'api_key' => $access_token,
                 'user_id' => $auto_assign_user->id,
                 'name' => "{$auto_assign_user->name}'s TRMNL",
@@ -204,7 +204,7 @@ Route::get('/setup', function (Request $request) {
         ], 404);
     }
 
-    $device = Device::where('mac_address', $mac_address)->first();
+    $device = Device::where('mac_address', mb_strtoupper($mac_address))->first();
 
     if (! $device) {
         // Check if there's a user with assign_new_devices enabled
@@ -219,7 +219,7 @@ Route::get('/setup', function (Request $request) {
 
             // Create a new device and assign it to this user
             $device = Device::create([
-                'mac_address' => $mac_address,
+                'mac_address' => mb_strtoupper($mac_address),
                 'api_key' => Str::random(22),
                 'user_id' => $auto_assign_user->id,
                 'name' => "{$auto_assign_user->name}'s TRMNL",
@@ -345,7 +345,7 @@ Route::post('/display/update', function (Request $request) {
 Route::post('/screens', function (Request $request) {
     $mac_address = $request->header('id');
     $access_token = $request->header('access-token');
-    $device = Device::where('mac_address', $mac_address)
+    $device = Device::where('mac_address', mb_strtoupper($mac_address ?? ''))
         ->where('api_key', $access_token)
         ->first();
 
diff --git a/tests/Feature/Api/DeviceEndpointsTest.php b/tests/Feature/Api/DeviceEndpointsTest.php
index 726f313..aff6758 100644
--- a/tests/Feature/Api/DeviceEndpointsTest.php
+++ b/tests/Feature/Api/DeviceEndpointsTest.php
@@ -954,3 +954,72 @@ test('setup endpoint handles non-existent device model gracefully', function ():
     expect($device)->not->toBeNull()
         ->and($device->device_model_id)->toBeNull();
 });
+
+test('setup endpoint matches MAC address case-insensitively', function (): void {
+    // Create device with lowercase MAC address
+    $device = Device::factory()->create([
+        'mac_address' => 'a1:b2:c3:d4:e5:f6',
+        'api_key' => 'test-api-key',
+        'friendly_id' => 'test-device',
+    ]);
+
+    // Request with uppercase MAC address should still match
+    $response = $this->withHeaders([
+        'id' => 'A1:B2:C3:D4:E5:F6',
+    ])->get('/api/setup');
+
+    $response->assertOk()
+        ->assertJson([
+            'status' => 200,
+            'api_key' => 'test-api-key',
+            'friendly_id' => 'test-device',
+            'message' => 'Welcome to TRMNL BYOS',
+        ]);
+});
+
+test('display endpoint matches MAC address case-insensitively', function (): void {
+    // Create device with lowercase MAC address
+    $device = Device::factory()->create([
+        'mac_address' => 'a1:b2:c3:d4:e5:f6',
+        'api_key' => 'test-api-key',
+        'current_screen_image' => 'test-image',
+    ]);
+
+    // Request with uppercase MAC address should still match
+    $response = $this->withHeaders([
+        'id' => 'A1:B2:C3:D4:E5:F6',
+        'access-token' => $device->api_key,
+        'rssi' => -70,
+        'battery_voltage' => 3.8,
+        'fw-version' => '1.0.0',
+    ])->get('/api/display');
+
+    $response->assertOk()
+        ->assertJson([
+            'status' => '0',
+            'filename' => 'test-image.bmp',
+        ]);
+});
+
+test('screens endpoint matches MAC address case-insensitively', function (): void {
+    Queue::fake();
+
+    // Create device with uppercase MAC address
+    $device = Device::factory()->create([
+        'mac_address' => 'A1:B2:C3:D4:E5:F6',
+        'api_key' => 'test-api-key',
+    ]);
+
+    // Request with lowercase MAC address should still match
+    $response = $this->withHeaders([
+        'id' => 'a1:b2:c3:d4:e5:f6',
+        'access-token' => $device->api_key,
+    ])->post('/api/screens', [
+        'image' => [
+            'content' => '<div>Test content</div>',
+        ],
+    ]);
+
+    $response->assertOk();
+    Queue::assertPushed(GenerateScreenJob::class);
+});