diff --git a/pyproject.toml b/pyproject.toml
index 5f2c1726..12a5db3d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -140,7 +140,7 @@ xfail_strict = true
 filterwarnings = [
     "error",
     # Apparently bqplot is using deprecated traitlets APIs
-    'ignore:\s+Sentinel is not a public part of the traitlets API:DeprecationWarning',
+    'ignore:\\s+Sentinel is not a public part of the traitlets API:DeprecationWarning',
     # ginga is using something from asdf that has been deprecated
     'ignore:AsdfInFits has been deprecated:DeprecationWarning',
     # ipyautoui generates this warning...