diff --git a/migrations/20250101000000_change_time_us_to_bigint.sql b/migrations/20250101000000_change_time_us_to_bigint.sql
index 6c01c2b..d94b4b7 100644
--- a/migrations/20250101000000_change_time_us_to_bigint.sql
+++ b/migrations/20250101000000_change_time_us_to_bigint.sql
@@ -1,4 +1,9 @@
 -- Change time_us from TEXT to BIGINT.
--- The existing values are stored as microsecond epoch strings and cast cleanly.
+-- First, replace any invalid values (like "undef") with 0.
+UPDATE posts
+SET time_us = '0'
+WHERE time_us = 'undef' OR time_us !~ '^\d+$';
+
+-- Now cast the column to BIGINT
 ALTER TABLE posts
     ALTER COLUMN time_us TYPE BIGINT USING time_us::BIGINT;