diff --git a/crates/storage-pg/migrations/20260122113523_compat_sessions_user_session_no_action.sql b/crates/storage-pg/migrations/20260122113523_compat_sessions_user_session_no_action.sql
new file mode 100644
index 000000000..d86ea2291
--- /dev/null
+++ b/crates/storage-pg/migrations/20260122113523_compat_sessions_user_session_no_action.sql
@@ -0,0 +1,19 @@
+-- Copyright 2026 Element Creations Ltd.
+--
+-- SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+-- Please see LICENSE files in the repository root for full details.
+
+-- Change compat_sessions.user_session_id FK from ON DELETE SET NULL to NO ACTION
+-- This ensures user_sessions cannot be deleted while compat_sessions reference them,
+-- which is required for backchannel logout propagation to work correctly.
+--
+-- Uses NOT VALID to avoid scanning the entire table while holding a lock.
+-- A separate migration will validate the constraint.
+
+ALTER TABLE compat_sessions
+    DROP CONSTRAINT compat_sessions_user_session_id_fkey,
+    ADD CONSTRAINT compat_sessions_user_session_id_fkey
+        FOREIGN KEY (user_session_id)
+        REFERENCES user_sessions (user_session_id)
+        ON DELETE NO ACTION
+        NOT VALID;
diff --git a/crates/storage-pg/migrations/20260122114353_compat_sessions_user_session_validate.sql b/crates/storage-pg/migrations/20260122114353_compat_sessions_user_session_validate.sql
new file mode 100644
index 000000000..4a5a7f23d
--- /dev/null
+++ b/crates/storage-pg/migrations/20260122114353_compat_sessions_user_session_validate.sql
@@ -0,0 +1,9 @@
+-- Copyright 2026 Element Creations Ltd.
+--
+-- SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+-- Please see LICENSE files in the repository root for full details.
+
+-- Validate the constraint added in the previous migration.
+-- This scans the table but does not hold an exclusive lock.
+ALTER TABLE compat_sessions
+    VALIDATE CONSTRAINT compat_sessions_user_session_id_fkey;