diff --git a/backend/alembic/versions/008_rename_rematch_to_game_choice.py b/backend/alembic/versions/008_rename_rematch_to_game_choice.py
index 5d63495..3b3cf39 100644
--- a/backend/alembic/versions/008_rename_rematch_to_game_choice.py
+++ b/backend/alembic/versions/008_rename_rematch_to_game_choice.py
@@ -17,15 +17,17 @@ depends_on = None
 
 def upgrade() -> None:
     # Update event type from 'rematch' to 'game_choice' in events table
+    # These UPDATE statements are idempotent - safe to run multiple times
     op.execute("UPDATE events SET type = 'game_choice' WHERE type = 'rematch'")
 
     # Update event_type in assignments table
     op.execute("UPDATE assignments SET event_type = 'game_choice' WHERE event_type = 'rematch'")
 
     # Update activity data that references rematch event
+    # Cast JSON to JSONB, apply jsonb_set, then cast back to JSON
     op.execute("""
         UPDATE activities
-        SET data = jsonb_set(data, '{event_type}', '"game_choice"')
+        SET data = jsonb_set(data::jsonb, '{event_type}', '"game_choice"')::json
         WHERE data->>'event_type' = 'rematch'
     """)
 
@@ -36,6 +38,6 @@ def downgrade() -> None:
     op.execute("UPDATE assignments SET event_type = 'rematch' WHERE event_type = 'game_choice'")
     op.execute("""
         UPDATE activities
-        SET data = jsonb_set(data, '{event_type}', '"rematch"')
+        SET data = jsonb_set(data::jsonb, '{event_type}', '"rematch"')::json
         WHERE data->>'event_type' = 'game_choice'
     """)