diff --git a/routes.py b/routes.py
index 6d0efe5..c3c63fa 100644
--- a/routes.py
+++ b/routes.py
@@ -19,32 +19,39 @@
 
 def _oauth_error_response(exc):
     """Return OAuth errors in a client-friendly way when redirect URI is valid."""
+    status_code = getattr(exc, 'status_code', 400) or 400
+    error_response = jsonify(error=exc.error, error_description=exc.description), status_code
+
     client_id = request.values.get('client_id')
     redirect_uri = request.values.get('redirect_uri')
     state = request.values.get('state')
 
     client = load_client(client_id) if client_id else None
-    if client:
-        if not redirect_uri:
-            redirect_uri = client.get_default_redirect_uri()
-        if redirect_uri and client.check_redirect_uri(redirect_uri):
-            parsed = urlparse(redirect_uri)
-            if parsed.scheme and parsed.netloc:
-                params = {'error': exc.error}
-                if exc.description:
-                    params['error_description'] = exc.description
-                if state:
-                    params['state'] = state
-
-                existing_query = dict(parse_qsl(parsed.query, keep_blank_values=True))
-                existing_query.update(params)
-                safe_redirect_uri = urlunparse(
-                    parsed._replace(query=urlencode(existing_query))
-                )
-                return redirect(safe_redirect_uri)
+    if not client:
+        return error_response
 
-    status_code = getattr(exc, 'status_code', 400) or 400
-    return jsonify(error=exc.error, error_description=exc.description), status_code
+    if not redirect_uri:
+        redirect_uri = client.get_default_redirect_uri()
+
+    if not redirect_uri or not client.check_redirect_uri(redirect_uri):
+        return error_response
+
+    parsed = urlparse(redirect_uri)
+    if not (parsed.scheme and parsed.netloc):
+        return error_response
+
+    params = {'error': exc.error}
+    if exc.description:
+        params['error_description'] = exc.description
+    if state:
+        params['state'] = state
+
+    existing_query = dict(parse_qsl(parsed.query, keep_blank_values=True))
+    existing_query.update(params)
+    safe_redirect_uri = urlunparse(
+        parsed._replace(query=urlencode(existing_query))
+    )
+    return redirect(safe_redirect_uri)
 
 
 def _resolve_smarthome_user_scope(req):