diff --git a/.gitignore b/.gitignore
index 8cf504324..a89f149ec 100644
--- a/.gitignore
+++ b/.gitignore
@@ -34,6 +34,7 @@ __pycache__/
 /logs
 /media_store/
 /uploads
+/homeserver-config-overrides.d
 
 # For direnv users
 /.envrc
diff --git a/changelog.d/15854.misc b/changelog.d/15854.misc
new file mode 100644
index 000000000..8c940dd9c
--- /dev/null
+++ b/changelog.d/15854.misc
@@ -0,0 +1 @@
+Fix the `devenv up` configuration which was ignoring the config overrides.
\ No newline at end of file
diff --git a/flake.nix b/flake.nix
index 8b7c0e6a5..bb42c9ff9 100644
--- a/flake.nix
+++ b/flake.nix
@@ -178,7 +178,7 @@
                   EOF
                 '';
                 # Start synapse when `devenv up` is run.
-                processes.synapse.exec = "poetry run python -m synapse.app.homeserver -c homeserver.yaml --config-directory homeserver-config-overrides.d";
+                processes.synapse.exec = "poetry run python -m synapse.app.homeserver -c homeserver.yaml -c homeserver-config-overrides.d";
 
                 # Define the perl modules we require to run SyTest.
                 #