diff --git a/alembic/versions/e1f2a3b4c5d6_add_template_id_to_glossaries.py b/alembic/versions/e1f2a3b4c5d6_add_template_id_to_glossaries.py
new file mode 100644
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+++ b/alembic/versions/e1f2a3b4c5d6_add_template_id_to_glossaries.py
@@ -0,0 +1,37 @@
+"""Add template_id column to glossaries table
+
+Revision ID: e1f2a3b4c5d6
+Revises: d0e1f2a3b4c5
+Create Date: 2026-06-01
+
+Tracks which preset template a glossary was imported from,
+enabling duplicate prevention on the import endpoint.
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers
+revision = "e1f2a3b4c5d6"
+down_revision = "d0e1f2a3b4c5"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "glossaries",
+        sa.Column("template_id", sa.String(50), nullable=True),
+    )
+    op.create_index(
+        "ix_glossaries_template_id",
+        "glossaries",
+        ["template_id"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_glossaries_template_id", table_name="glossaries")
+    op.drop_column("glossaries", "template_id")