diff --git a/src/database.py b/src/database.py
index 8119aec..3c44c65 100644
--- a/src/database.py
+++ b/src/database.py
@@ -157,10 +157,13 @@ class Database:
             logger.error(f"Error creating test user: {e}")
 
     def _create_superadmin(self, conn: sqlite3.Connection, email: str):
-        """Create or promote superadmin user."""
+        """Create or promote superadmin user (case-insensitive match)."""
         try:
             username = email.split('@')[0]
-            cursor = conn.execute('SELECT id, role FROM users WHERE username = ? OR email = ?', (username, email))
+            cursor = conn.execute(
+                'SELECT id, role FROM users WHERE LOWER(username) = LOWER(?) OR LOWER(email) = LOWER(?)',
+                (username, email),
+            )
             row = cursor.fetchone()
             if row:
                 if row['role'] != 'admin':