diff --git a/docs/conf.py b/docs/conf.py
index 4f5d4a1a..94db96f8 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -305,6 +305,7 @@ def get_minor_version(package_name: str) -> str:
     "https://github.com/orgs/ComPWA/projects/6",  # private
     "https://ieeexplore.ieee.org/document/6312940",  # 401
     "https://open.vscode.dev",
+    "https://via.placeholder.com",  # irregular timeout
     "https://www.andiamo.co.uk/resources/iso-language-codes",  # 443, but works
 ]