diff --git a/tailbone/templates/forms/deform_buefy.mako b/tailbone/templates/forms/deform_buefy.mako
index c70c624c..5ca8b1ac 100644
--- a/tailbone/templates/forms/deform_buefy.mako
+++ b/tailbone/templates/forms/deform_buefy.mako
@@ -96,7 +96,7 @@
                   % elif isinstance(field.schema.typ, deform.FileData):
                       field_model_${field.name}: null,
                   % else:
-                      field_model_${field.name}: ${json.dumps(field.cstruct)|n},
+                      field_model_${field.name}: ${'null' if field.cstruct is colander.null else json.dumps(field.cstruct)|n},
                   % endif
               % endif
           % endfor