diff --git a/django/oldforms/__init__.py b/django/oldforms/__init__.py
index b437109596..decf0f7064 100644
--- a/django/oldforms/__init__.py
+++ b/django/oldforms/__init__.py
@@ -958,7 +958,9 @@ class USStateField(TextField):
             raise validators.CriticalValidationError, e.messages
 
     def html2python(data):
-        return data.upper() # Should always be stored in upper case
+        if data:
+            return data.upper() # Should always be stored in upper case
+        return data
     html2python = staticmethod(html2python)
 
 class CommaSeparatedIntegerField(TextField):