diff --git a/test/test_helper.exs b/test/test_helper.exs
index 23d4fb15..9169ea92 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -38,6 +38,12 @@ end
 # DBConnection.Ownership from the app env and initializes with it.
 {:ok, _} = Application.ensure_all_started(:microwaveprop)
 
+# stream_data is a test-only dep — its ebin is on the code path from the
+# wildcard above, but the application isn't started. `check all` etc.
+# call Application.fetch_env!(:stream_data, :initial_size), which needs
+# the app to be loaded.
+Application.ensure_all_started(:stream_data)
+
 # :auto mode lets every process (including background Tasks started by
 # Application.init and Oban workers) auto-checkout from the sandbox.
 # DataCase.setup_sandbox/1 still calls start_owner!/2 for per-test