diff --git a/requirements.in b/requirements.in
index 6f14a4595..37d41edc9 100644
--- a/requirements.in
+++ b/requirements.in
@@ -28,5 +28,6 @@ git+https://github.com/alphagov/notifications-utils.git@44.1.0#egg=notifications
 git+https://github.com/alphagov/govuk-frontend-jinja.git@v0.5.8-alpha#egg=govuk-frontend-jinja==0.5.8-alpha
 
 # gds-metrics requires prometheseus 0.2.0, override that requirement as later versions bring significant performance gains
-prometheus-client==0.10.0
+# version 0.10.0 introduced exceptions when workers crashed due to deprecating lower case `prometheus_multiproc_dir`.
+prometheus-client>=0.9.0,!=0.10.0
 gds-metrics==0.2.4
diff --git a/requirements.txt b/requirements.txt
index debcea521..137ae320c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -118,7 +118,7 @@ packaging==20.9
     # via bleach
 phonenumbers==8.12.20
     # via notifications-utils
-prometheus-client==0.10.0
+prometheus-client==0.9.0
     # via
     #   -r requirements.in
     #   gds-metrics