diff --git a/changelog.d/3947.misc b/changelog.d/3947.misc
new file mode 100644
index 000000000000..5a9a22bed992
--- /dev/null
+++ b/changelog.d/3947.misc
@@ -0,0 +1 @@
+Require attrs 16.0.0 or later
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 0d8de600cfa7..c779f69fa07f 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -58,7 +58,9 @@
     "phonenumbers>=8.2.0": ["phonenumbers"],
     "six": ["six"],
     "prometheus_client": ["prometheus_client"],
-    "attrs": ["attr"],
+
+    # we use attr.s(slots), which arrived in 16.0.0
+    "attrs>=16.0.0": ["attr>=16.0.0"],
     "netaddr>=0.7.18": ["netaddr"],
 }