diff --git a/hindsight-api-slim/hindsight_api/alembic/versions/f6g7h8i9j0k1_chunk_fk_cascade_delete.py b/hindsight-api-slim/hindsight_api/alembic/versions/f6g7h8i9j0k1_chunk_fk_cascade_delete.py
new file mode 100644
index 00000000..f0311496
--- /dev/null
+++ b/hindsight-api-slim/hindsight_api/alembic/versions/f6g7h8i9j0k1_chunk_fk_cascade_delete.py
@@ -0,0 +1,38 @@
+"""chunk_fk_cascade_delete
+
+Revision ID: f6g7h8i9j0k1
+Revises: e5f6g7h8i9j0
+Create Date: 2026-03-16 00:00:00.000000
+
+"""
+
+from collections.abc import Sequence
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "f6g7h8i9j0k1"
+down_revision: str | Sequence[str] | None = "e5f6g7h8i9j0"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    """Change memory_units.chunk_id FK from SET NULL to CASCADE.
+
+    When a document is deleted the CASCADE reaches chunks first; with SET NULL
+    the memory_units rows survived with chunk_id = NULL, leaving ghost records.
+    Switching to CASCADE ensures they are removed together with their chunk.
+    """
+    op.drop_constraint("memory_units_chunk_fkey", "memory_units", type_="foreignkey")
+    op.create_foreign_key(
+        "memory_units_chunk_fkey", "memory_units", "chunks", ["chunk_id"], ["chunk_id"], ondelete="CASCADE"
+    )
+
+
+def downgrade() -> None:
+    """Revert to SET NULL behaviour."""
+    op.drop_constraint("memory_units_chunk_fkey", "memory_units", type_="foreignkey")
+    op.create_foreign_key(
+        "memory_units_chunk_fkey", "memory_units", "chunks", ["chunk_id"], ["chunk_id"], ondelete="SET NULL"
+    )