diff --git a/migrations/000_baseline.sql b/migrations/000_baseline.sql
index dc7ddc8..3eeee7d 100644
--- a/migrations/000_baseline.sql
+++ b/migrations/000_baseline.sql
@@ -155,7 +155,7 @@ CREATE TABLE IF NOT EXISTS `saved_filters` (
   UNIQUE KEY `unique_user_filter_name` (`user_id`,`filter_name`),
   KEY `idx_user_filters` (`user_id`,`is_default`),
   CONSTRAINT `saved_filters_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`user_id`) ON DELETE CASCADE
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;
 
 -- ============ status_transitions ============
 CREATE TABLE IF NOT EXISTS `status_transitions` (
@@ -185,7 +185,7 @@ CREATE TABLE IF NOT EXISTS `ticket_attachments` (
   KEY `idx_attachments_ticket` (`ticket_id`),
   KEY `idx_attachments_uploaded_by` (`uploaded_by`),
   CONSTRAINT `ticket_attachments_ibfk_1` FOREIGN KEY (`uploaded_by`) REFERENCES `users` (`user_id`) ON DELETE SET NULL
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;
 
 -- ============ ticket_comments ============
 CREATE TABLE IF NOT EXISTS `ticket_comments` (
diff --git a/migrations/002_fix_collation_consistency.sql b/migrations/002_fix_collation_consistency.sql
new file mode 100644
index 0000000..5f366ec
--- /dev/null
+++ b/migrations/002_fix_collation_consistency.sql
@@ -0,0 +1,30 @@
+-- Fix collation inconsistency on saved_filters and ticket_attachments
+--
+-- README.md Developer Notes #12: "Database collation: Use
+-- utf8mb4_general_ci (not unicode_ci) for new tables." These two tables
+-- were created with utf8mb4_unicode_ci instead, inconsistent with every
+-- other table in the schema. Mixed collations don't break anything by
+-- themselves, but any future query joining/comparing these columns
+-- against general_ci columns needs explicit COLLATE casts or hits
+-- "Illegal mix of collations" errors.
+--
+-- Safe to re-run.
+
+ALTER TABLE `saved_filters`
+    CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;
+
+-- saved_filters.filter_criteria is pinned to utf8mb4_bin (for the
+-- json_valid() CHECK constraint) — restore that after the table-wide
+-- CONVERT TO above, which resets it to general_ci. MariaDB drops the
+-- inline CHECK when the column is MODIFYed, so re-add it explicitly.
+ALTER TABLE `saved_filters`
+    MODIFY COLUMN `filter_criteria` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL;
+
+ALTER TABLE `saved_filters`
+    DROP CONSTRAINT IF EXISTS `saved_filters_filter_criteria_json`;
+
+ALTER TABLE `saved_filters`
+    ADD CONSTRAINT `saved_filters_filter_criteria_json` CHECK (json_valid(`filter_criteria`));
+
+ALTER TABLE `ticket_attachments`
+    CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;