diff --git a/backend/k8s/db.yaml b/backend/k8s/db.yaml
index 8c498e01..5475f6b6 100644
--- a/backend/k8s/db.yaml
+++ b/backend/k8s/db.yaml
@@ -54,7 +54,7 @@ spec:
             claimName: test-observer-db
       containers:
         - name: test-observer-db
-          image: postgres:15.2
+          image: postgres:14
           volumeMounts:
             - name: test-observer-db
               mountPath: /var/lib/postgresql/data
diff --git a/backend/migrations/versions/2023_06_20_1000-b33ee8dd41b1_use_nulls_not_distinct.py b/backend/migrations/versions/2023_06_20_1000-b33ee8dd41b1_use_nulls_not_distinct.py
deleted file mode 100644
index d82cf95d..00000000
--- a/backend/migrations/versions/2023_06_20_1000-b33ee8dd41b1_use_nulls_not_distinct.py
+++ /dev/null
@@ -1,33 +0,0 @@
-"""Use nulls not distinct
-
-Revision ID: b33ee8dd41b1
-Revises: 6a80dad01d24
-Create Date: 2023-06-20 10:00:07.676129+00:00
-
-"""
-from alembic import op
-
-
-# revision identifiers, used by Alembic.
-revision = "b33ee8dd41b1"
-down_revision = "6a80dad01d24"
-branch_labels = None
-depends_on = None
-
-
-def upgrade() -> None:
-    op.execute(
-        "ALTER TABLE artefact_build "
-        "DROP CONSTRAINT IF EXISTS artefact_build_artefact_id_architecture_revision_key"
-        ", ADD CONSTRAINT unique_artefact_build "
-        "UNIQUE NULLS NOT DISTINCT (artefact_id, architecture, revision);"
-    )
-
-
-def downgrade() -> None:
-    op.execute(
-        "ALTER TABLE artefact_build "
-        "DROP CONSTRAINT IF EXISTS unique_artefact_build"
-        ", ADD CONSTRAINT artefact_build_artefact_id_architecture_revision_key "
-        "UNIQUE (artefact_id, architecture, revision);"
-    )
diff --git a/backend/migrations/versions/2023_07_11_1148-158244992900_disallow_multiple_artefact_builds_with_.py b/backend/migrations/versions/2023_07_11_1148-158244992900_disallow_multiple_artefact_builds_with_.py
new file mode 100644
index 00000000..ac0b636b
--- /dev/null
+++ b/backend/migrations/versions/2023_07_11_1148-158244992900_disallow_multiple_artefact_builds_with_.py
@@ -0,0 +1,32 @@
+"""disallow multiple artefact builds with null revision
+
+Revision ID: 158244992900
+Revises: b33ee8dd41b1
+Create Date: 2023-07-11 11:48:49.777726+00:00
+
+"""
+from alembic import op
+
+
+# revision identifiers, used by Alembic.
+revision = "158244992900"
+down_revision = "6a80dad01d24"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_index(
+        "unique_artefact_build_null_revision",
+        "artefact_build",
+        ["artefact_id", "architecture"],
+        unique=True,
+        postgresql_where=("revision IS NULL"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_index(
+        "unique_artefact_build_null_revision",
+        "artefact_build",
+    )