diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index d91f9c29187..6329fc34036 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -155,7 +155,7 @@ jobs:
         uses: matrix-org/setup-python-poetry@v1
         with:
           # We want to make use of type hints in optional dependencies too.
-          extras: all
+          extras: "all scim"
           # We have seen odd mypy failures that were resolved when we started
           # installing the project again:
           # https://github.com/matrix-org/synapse/pull/15376#issuecomment-1498983775