diff --git a/optional-requirements.txt b/optional-requirements.txt
index 5b9ecd5..f314fa9 100644
--- a/optional-requirements.txt
+++ b/optional-requirements.txt
@@ -9,7 +9,7 @@ python-olm>=3,<4
 unpaddedbase64>=1,<3
 
 #/metrics
-prometheus_client>=0.6,<0.20
+prometheus_client>=0.6,<0.22
 
 #/proxy
 pysocks