diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 001c798fe..faf6dfdb8 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -57,6 +57,7 @@ REQUIREMENTS = {
     "phonenumbers>=8.2.0": ["phonenumbers"],
     "six": ["six"],
     "prometheus_client": ["prometheus_client"],
+    "attr": ["attr"],
 }
 
 CONDITIONAL_REQUIREMENTS = {