diff --git a/test/test_helper.exs b/test/test_helper.exs
index eb666866..41ac09ec 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -39,6 +39,14 @@ end
 # DBConnection.Ownership from the app env and initializes with it.
 {:ok, _} = Application.ensure_all_started(:microwaveprop)
 
+# Clean up any rows left behind by a crashed or killed prior run.
+# The sandbox rolls back per-test, but if the suite itself crashes
+# mid-run, committed data persists and causes count-mismatch failures
+# in the next run. Wipe known test-data tables before each suite.
+for table <- ~w(contacts hrrr_fetch_tasks iemre_observations oban_jobs) do
+  Microwaveprop.Repo.delete_all(table)
+end
+
 # 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