diff --git a/requirements.txt b/requirements.txt
index b6d8b89..05a8ebf 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,6 +4,9 @@ redis
 # (generic Mongo find_one/distinct/aggregate methods) — not in 1.12.2 yet.
 # Local dev uses an editable install of the local checkout (feature/SIENTIAPDE-1590).
 sientia_do==1.12.2
+# TEST ONLY (SIENTIAPDE-1975 dev test): SQLAlchemy 2.1 makes psycopg (v3) the default driver for
+# postgresql:// URLs; sientia_do 1.12.2 builds that URL and ships only psycopg2-binary.
+sqlalchemy<2.1
 prometheus_client
 pymongo
 nats-py>=2.6