diff --git a/CHANGELOG.md b/CHANGELOG.md
index f0fba51..f0a4e22 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,7 +13,15 @@ getaggte Releases (Kanal `stable`, optional `beta`) — niemals Entwicklungs-Bui
 
 _Keine offenen Änderungen — der nächste Stand wird hier gesammelt und als `vX.Y.Z` getaggt._
 
-## [0.9.53] - 2026-06-22
+## [0.9.54] - 2026-06-22
+
+### Behoben
+- **Datei-Manager: „undefined is not valid JSON" beim Öffnen mancher Dateien.** Öffnete man eine
+  **Binär-/Nicht-UTF-8-Datei**, landeten deren Rohbytes in einer Livewire-Eigenschaft. Livewire
+  JSON-kodiert seinen Zustand, und ungültiges UTF-8 lässt `json_encode` scheitern → der Client bekam
+  eine leere Antwort und warf den Fehler. Binär-/zu-große Dateien werden jetzt nicht mehr als Inhalt
+  gebunden (es erscheint der Binär-Hinweis), sodass der Zustand immer gültiges JSON bleibt — sowohl
+  im Editor als auch in der zugrunde liegenden Datei-Lese-Funktion abgesichert.
 
 ### Behoben
 - **JavaScript-Fehler im Datei-Manager (und anderen Listen): „pending is not defined".** In Listen
diff --git a/app/Livewire/Modals/FileEditor.php b/app/Livewire/Modals/FileEditor.php
index c64b47d..386f9db 100644
--- a/app/Livewire/Modals/FileEditor.php
+++ b/app/Livewire/Modals/FileEditor.php
@@ -91,9 +91,12 @@ class FileEditor extends ModalComponent
                 $this->loadImage($server, $sftp);
             } else {
                 $r = $fleet->readFile($server, $this->path);
-                $this->content = $r['content'];
                 $this->binary = $r['binary'];
                 $this->tooBig = $r['tooBig'];
+                // Never bind raw non-UTF-8 bytes to a public property: Livewire JSON-encodes the
+                // snapshot and invalid UTF-8 makes json_encode fail, so the client receives an empty
+                // response ("undefined is not valid JSON"). Binary/oversize files show a notice instead.
+                $this->content = ($r['binary'] || $r['tooBig']) ? '' : $r['content'];
             }
         } catch (Throwable $e) {
             $this->error = $e->getMessage();
diff --git a/app/Services/FleetService.php b/app/Services/FleetService.php
index a30b063..3134114 100644
--- a/app/Services/FleetService.php
+++ b/app/Services/FleetService.php
@@ -561,7 +561,9 @@ class FleetService
             $content = $size > $maxBytes ? '' : (string) $sftp->get($path);
             $binary = $content !== '' && (str_contains(substr($content, 0, 8000), "\0") || ! mb_check_encoding($content, 'UTF-8'));
 
-            return ['content' => $content, 'binary' => $binary, 'tooBig' => $size > $maxBytes];
+            // Never hand back raw non-UTF-8 bytes: bound to a Livewire public property they break the
+            // JSON snapshot ("undefined is not valid JSON"). The caller renders a binary notice instead.
+            return ['content' => $binary ? '' : $content, 'binary' => $binary, 'tooBig' => $size > $maxBytes];
         } finally {
             $sftp->disconnect();
         }
diff --git a/config/clusev.php b/config/clusev.php
index b5066e2..9b619fe 100644
--- a/config/clusev.php
+++ b/config/clusev.php
@@ -2,7 +2,7 @@
 
 return [
     // First tagged release is v0.1.0 (semantic, not -dev).
-    'version' => '0.9.53',
+    'version' => '0.9.54',
 
     // Deployed commit + branch. install.sh bakes these into .env from the host's .git (the prod
     // image ships no .git); the Versions page prefers them and falls back to a live .git read in
diff --git a/tests/Feature/FileEditorBinaryTest.php b/tests/Feature/FileEditorBinaryTest.php
new file mode 100644
index 0000000..3dd485d
--- /dev/null
+++ b/tests/Feature/FileEditorBinaryTest.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Livewire\Modals\FileEditor;
+use App\Models\Server;
+use App\Models\User;
+use App\Services\FleetService;
+use App\Support\Ssh\Sftp;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Livewire\Livewire;
+use Mockery;
+use Tests\TestCase;
+
+/**
+ * Binary / non-UTF-8 file content must never reach the editor's public $content property: bound into
+ * Livewire's JSON snapshot, invalid UTF-8 makes json_encode fail and the client sees an empty response
+ * ("undefined is not valid JSON"). The editor blanks it and shows a binary notice instead.
+ */
+class FileEditorBinaryTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->actingAs(User::factory()->create(['must_change_password' => false]));
+        $this->app->instance(Sftp::class, Mockery::mock(Sftp::class)); // unused for text files, just resolvable
+    }
+
+    public function test_load_blanks_binary_content_to_keep_the_snapshot_valid(): void
+    {
+        $server = Server::create(['name' => 's', 'ip' => '10.0.0.9', 'ssh_port' => 22, 'status' => 'online']);
+
+        $fleet = Mockery::mock(FleetService::class);
+        $fleet->shouldReceive('readFile')->andReturn(['content' => "\xff\xfe\x00\x80raw-binary", 'binary' => true, 'tooBig' => false]);
+        $this->app->instance(FleetService::class, $fleet);
+
+        Livewire::test(FileEditor::class, ['serverId' => $server->id, 'path' => '/tmp/x.bin', 'name' => 'x.bin'])
+            ->call('load')
+            ->assertSet('binary', true)
+            ->assertSet('content', '');   // raw non-UTF-8 bytes never bound to the property
+    }
+
+    public function test_load_keeps_valid_text_content(): void
+    {
+        $server = Server::create(['name' => 's', 'ip' => '10.0.0.9', 'ssh_port' => 22, 'status' => 'online']);
+
+        $fleet = Mockery::mock(FleetService::class);
+        $fleet->shouldReceive('readFile')->andReturn(['content' => "hello = welt\n", 'binary' => false, 'tooBig' => false]);
+        $this->app->instance(FleetService::class, $fleet);
+
+        Livewire::test(FileEditor::class, ['serverId' => $server->id, 'path' => '/etc/x.conf', 'name' => 'x.conf'])
+            ->call('load')
+            ->assertSet('binary', false)
+            ->assertSet('content', "hello = welt\n");
+    }
+}