diff -ur synapse-0.99.5.2/synapse/python_dependencies.py synapse-0.99.5.2.patched/synapse/python_dependencies.py
--- synapse-0.99.5.2/synapse/python_dependencies.py	2019-05-31 01:29:47.000000000 +1000
+++ synapse-0.99.5.2.patched/synapse/python_dependencies.py	2019-06-08 16:21:33.986360990 +1000
@@ -67,7 +67,7 @@
     "six>=1.10",
     # prometheus_client 0.4.0 changed the format of counter metrics
     # (cf https://github.com/matrix-org/synapse/issues/4001)
-    "prometheus_client>=0.0.18,<0.4.0",
+    "prometheus_client>=0.0.18",
 
     # we use attr.s(slots), which arrived in 16.0.0
     # Twisted 18.7.0 requires attrs>=17.4.0