diff --git a/backend/src/services/settingsService.js b/backend/src/services/settingsService.js
index 6200bb7..fbc3b41 100644
--- a/backend/src/services/settingsService.js
+++ b/backend/src/services/settingsService.js
@@ -949,7 +949,9 @@ class SettingsService {
     const ripMode = String(map.makemkv_rip_mode || 'mkv').trim().toLowerCase() === 'backup'
       ? 'backup'
       : 'mkv';
-    const sourceArg = this.resolveSourceArg(map, deviceInfo);
+    const sourceArg = ripMode === 'backup'
+      ? this.resolveBackupSourceArg(map, deviceInfo)
+      : this.resolveSourceArg(map, deviceInfo);
     const rawSelectedTitleId = normalizeNonNegativeInteger(options?.selectedTitleId);
     const parsedExtra = splitArgs(map.makemkv_rip_extra_args);
     let extra = [];
@@ -1008,6 +1010,20 @@ class SettingsService {
     return { cmd, args: [...baseArgs, ...extra] };
   }
 
+  resolveBackupSourceArg(map, deviceInfo = null) {
+    const rawDeviceIndex = Number(deviceInfo?.index);
+    if (Number.isFinite(rawDeviceIndex) && rawDeviceIndex >= 0) {
+      return `disc:${Math.trunc(rawDeviceIndex)}`;
+    }
+
+    const rawConfiguredIndex = Number(map?.makemkv_source_index);
+    if (Number.isFinite(rawConfiguredIndex) && rawConfiguredIndex >= 0) {
+      return `disc:${Math.trunc(rawConfiguredIndex)}`;
+    }
+
+    return 'disc:0';
+  }
+
   async buildMakeMKVRegisterConfig() {
     const map = await this.getSettingsMap();
     const registrationKey = String(map.makemkv_registration_key || '').trim();