diff --git a/setup.py b/setup.py
index 4a0985fd..79e0d7e3 100644
--- a/setup.py
+++ b/setup.py
@@ -29,6 +29,8 @@
         install_requires=[
             "incremental",
             "requests >= 2.1.0",
+            # Require a recent Hyperlink as some old versions have serious bugs.
+            "hyperlink >= 19.0.0",
             "six",
             "Twisted[tls] >= 16.4.0 ; python_version < '3.7'",
             "Twisted[tls] >= 18.7.0 ; python_version >= '3.7'",