diff --git a/install.sh b/install.sh
index 8ae16a3..1cbea88 100755
--- a/install.sh
+++ b/install.sh
@@ -440,26 +440,18 @@ if os.path.exists(var_app):
 
 for td in target_dirs:
     if os.path.exists(td):
-        # 1. Set preferences.json theme to defaultDark
-        pref_file = os.path.join(td, 'preferences.json')
-        try:
-            pdata = {}
-            if os.path.exists(pref_file):
-                with open(pref_file, 'r', encoding='utf-8') as f:
-                    pdata = json.load(f)
-            pdata['theme'] = 'defaultDark'
-            with open(pref_file, 'w', encoding='utf-8') as f:
-                json.dump(pdata, f, indent=2)
-        except Exception: pass
-
-        # 2. Clean up corrupted config.json / settings.json
-        for bad in ['config.json', 'settings.json']:
-            bp = os.path.join(td, bad)
-            if os.path.exists(bp):
+        # Clean up / sanitize invalid Electron theme strings in config.json, preferences.json, settings.json
+        for fn in ['config.json', 'preferences.json', 'settings.json']:
+            fp = os.path.join(td, fn)
+            if os.path.exists(fp):
                 try:
-                    with open(bp, 'r', encoding='utf-8') as f: bd = json.load(f)
-                    if isinstance(bd, dict) and list(bd.keys()) == ['theme']:
-                        os.remove(bp)
+                    with open(fp, 'r', encoding='utf-8') as f: data = json.load(f)
+                    if isinstance(data, dict):
+                        if list(data.keys()) == ['theme'] and data['theme'] not in ['dark', 'light', 'system', 'defaultDark', 'defaultLight']:
+                            os.remove(fp)
+                        elif 'theme' in data and data['theme'] not in ['dark', 'light', 'system', 'defaultDark', 'defaultLight']:
+                            data['theme'] = 'dark'
+                            with open(fp, 'w', encoding='utf-8') as f: json.dump(data, f, indent=2)
                 except Exception: pass
 " 2>/dev/null || true
 }
diff --git a/quickshell/services/python/theme_sync.py b/quickshell/services/python/theme_sync.py
index 9dde055..02f0c23 100644
--- a/quickshell/services/python/theme_sync.py
+++ b/quickshell/services/python/theme_sync.py
@@ -1298,15 +1298,21 @@ def sync_feishin(bg, surface, current_line, fg, accent, sub_accent, is_dark, var
                 with open(os.path.join(themes_dir, "quickshell.json"), 'w', encoding='utf-8') as f:
                     json.dump(qs_json, f, indent=2)
 
-            # Repair/remove any corrupted config.json or settings.json files created by previous bad writes
-            for bad_file_name in ['config.json', 'settings.json']:
-                bad_path = os.path.join(base_dir, bad_file_name)
-                if os.path.exists(bad_path):
+            # Ensure config.json, preferences.json, and settings.json maintain valid Electron themeSource ("dark" or "light")
+            valid_electron_theme = "dark" if is_dark else "light"
+            for conf_file_name in ['config.json', 'preferences.json', 'settings.json']:
+                conf_path = os.path.join(base_dir, conf_file_name)
+                if os.path.exists(conf_path):
                     try:
-                        with open(bad_path, 'r', encoding='utf-8') as f:
-                            bad_data = json.load(f)
-                        if isinstance(bad_data, dict) and list(bad_data.keys()) == ['theme']:
-                            os.remove(bad_path)
+                        with open(conf_path, 'r', encoding='utf-8') as f:
+                            cdata = json.load(f)
+                        if isinstance(cdata, dict):
+                            if list(cdata.keys()) == ['theme'] and cdata['theme'] not in ['dark', 'light', 'system', 'defaultDark', 'defaultLight']:
+                                os.remove(conf_path)
+                            elif 'theme' in cdata and cdata['theme'] not in ['dark', 'light', 'system', 'defaultDark', 'defaultLight']:
+                                cdata['theme'] = valid_electron_theme
+                                with open(conf_path, 'w', encoding='utf-8') as f:
+                                    json.dump(cdata, f, indent=2)
                     except Exception:
                         pass
         except Exception: