diff --git a/database/migrations/003_unique_posts.ts b/database/migrations/003_unique_posts.ts
new file mode 100644
index 0000000..533a19c
--- /dev/null
+++ b/database/migrations/003_unique_posts.ts
@@ -0,0 +1,19 @@
+import { Kysely } from "@kysely/kysely"
+
+const up = async (db: Kysely<unknown>) => {
+  await db.schema
+    .createIndex("idx_at_proto_uri")
+    .on("posts")
+    .column("at_proto_uri")
+    .unique()
+    .execute()
+}
+
+const down = async (db: Kysely<unknown>) => {
+  await db.schema
+    .dropIndex("idx_at_proto_uri")
+    .on("posts")
+    .execute()
+}
+
+export default { up, down }
diff --git a/database/migrator.ts b/database/migrator.ts
index 08ca815..174ee13 100644
--- a/database/migrator.ts
+++ b/database/migrator.ts
@@ -1,10 +1,12 @@
 import { type Migration, type MigrationProvider } from "@kysely/kysely"
 import migration1 from "./migrations/001_initial.ts"
 import migration2 from "./migrations/002_refresh_token.ts"
+import migration3 from "./migrations/003_unique_posts.ts"
 
 const migrations = {
   "001_initial": migration1,
   "002_refresh_token": migration2,
+  "003_unique_posts": migration3,
 } satisfies Record<string, Migration>
 
 export const migrationProvider = {