diff --git a/alembic/versions/a192abbf4091_add_manufacturers_table.py b/alembic/versions/a192abbf4091_add_manufacturers_table.py
index 9d933f2..af18123 100644
--- a/alembic/versions/a192abbf4091_add_manufacturers_table.py
+++ b/alembic/versions/a192abbf4091_add_manufacturers_table.py
@@ -28,12 +28,19 @@ def upgrade() -> None:
         sa.Column("logo_url", sa.String(), nullable=True),
         sa.PrimaryKeyConstraint("id"),
     )
+    # batch_alter_table's alter_column doesn't emit CREATE TYPE for the new
+    # Enum on its own (unlike create_table, which ties enum creation to the
+    # table-create DDL event) - create it explicitly first, or Postgres fails
+    # with `type "uncseries" does not exist`. checkfirst / no-op on SQLite.
+    uncseries = sa.Enum("UNC", "UNF", "UNEF", "UN", "UNS", name="uncseries")
+    uncseries.create(op.get_bind(), checkfirst=True)
     with op.batch_alter_table("unc_threads", schema=None) as batch_op:
         batch_op.alter_column(
             "series",
             existing_type=sa.VARCHAR(length=8),
-            type_=sa.Enum("UNC", "UNF", "UNEF", "UN", "UNS", name="uncseries"),
+            type_=uncseries,
             existing_nullable=False,
+            postgresql_using="series::uncseries",
         )
 
     # ### end Alembic commands ###
@@ -47,7 +54,9 @@ def downgrade() -> None:
             existing_type=sa.Enum("UNC", "UNF", "UNEF", "UN", "UNS", name="uncseries"),
             type_=sa.VARCHAR(length=8),
             existing_nullable=False,
+            postgresql_using="series::varchar(8)",
         )
+    sa.Enum(name="uncseries").drop(op.get_bind(), checkfirst=True)
 
     op.drop_table("manufacturers")
     # ### end Alembic commands ###