diff --git a/README.md b/README.md
index 340752ca7..74501784e 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ GOV.UK Notify admin application - https://www.notifications.service.gov.uk/
 
 ### Python version
 
-At the moment we run Python 3.6 in production.
+At the moment we run Python 3.9 in production.
 
 ### NPM packages
 
diff --git a/runtime.txt b/runtime.txt
index 62ce9c02a..305091cae 100644
--- a/runtime.txt
+++ b/runtime.txt
@@ -1 +1 @@
-python-3.6.x
+python-3.9.x