diff --git a/deform/field.py b/deform/field.py
index 04743c37..0a470bdd 100644
--- a/deform/field.py
+++ b/deform/field.py
@@ -424,8 +424,8 @@ def default_item_css_class(self):
             .encode("ascii", "ignore")
             .decode("ascii")
         )
-        css_class = re.sub("[^\w\s-]", "", css_class).strip().lower()  # noQA
-        css_class = re.sub("[-\s]+", "-", css_class)  # noQA
+        css_class = re.sub(r"[^\w\s-]", "", css_class).strip().lower()  # noQA
+        css_class = re.sub(r"[-\s]+", "-", css_class)  # noQA
         return "item-%s" % css_class
 
     def get_widget_requirements(self):