diff --git a/bootstrapform/templatetags/bootstrap.py b/bootstrapform/templatetags/bootstrap.py
index 8c36c18..f68c37e 100644
--- a/bootstrapform/templatetags/bootstrap.py
+++ b/bootstrapform/templatetags/bootstrap.py
@@ -49,7 +49,7 @@ def bootstrap_horizontal(element, label_cols={}):
 
     return render(element, markup_classes)
 
-
+@register.filter
 def add_input_classes(field):
     if not is_checkbox(field) and not is_multiple_checkbox(field) and not is_radio(field) \
         and not is_file(field):