diff --git a/lab4/twidder/server.py b/lab4/twidder/server.py
index 0a3dac15be38ff54f49bfb95e2fdb2ebc57ca502..b7a28edc12eaeaed844d79efdb67bbcda0415f75 100644
--- a/lab4/twidder/server.py
+++ b/lab4/twidder/server.py
@@ -104,7 +104,7 @@ def is_signup_form_valid(data):
         return False
 
     for field in data:
-        if not (len(data[field].strip())):
+        if not (len(str(data[field]).strip())):
             # string is empty
             return False