diff --git a/prisma/migrations/20260324100000_add_ci_username_unique_index/migration.sql b/prisma/migrations/20260324100000_add_ci_username_unique_index/migration.sql
new file mode 100644
index 00000000..e12aaa06
--- /dev/null
+++ b/prisma/migrations/20260324100000_add_ci_username_unique_index/migration.sql
@@ -0,0 +1,4 @@
+-- Add case-insensitive unique indexes to prevent TOCTOU race conditions
+-- These ensure the database enforces uniqueness regardless of casing
+CREATE UNIQUE INDEX "users_username_ci_unique" ON "users" (LOWER("username"));
+CREATE UNIQUE INDEX "users_email_ci_unique" ON "users" (LOWER("email"));