diff --git a/src/concurrency/forms.py b/src/concurrency/forms.py
index 1ca2fbe..e7ea7d2 100644
--- a/src/concurrency/forms.py
+++ b/src/concurrency/forms.py
@@ -91,7 +91,7 @@ def __repr__(self):
             return ''
 
 
-class VersionField(forms.IntegerField):
+class VersionField(forms.Field):
     widget = HiddenInput  # Default widget to use when rendering this type of Field.
     hidden_widget = HiddenInput  # Default widget to use when rendering this as "hidden".
 
@@ -115,10 +115,11 @@ def prepare_value(self, value):
         return SignedValue(self._signer.sign(value))
 
     def to_python(self, value):
-        try:
-            if value not in (None, '', 'None'):
-                return int(self._signer.unsign(str(value)))
+        value = super().to_python(value)
+        if value in self.empty_values:
             return 0
+        try:
+            return int(self._signer.unsign(str(value)))
         except (BadSignature, ValueError):
             raise VersionError(value)