diff --git a/src/config.ts b/src/config.ts
index 440cd26..ba36898 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -126,6 +126,10 @@ const Conf = {
       'system',
     ];
   },
+  /** Whether registrations are open or closed. */
+  get registrations() {
+    return optionalBooleanSchema.parse(Deno.env.get('DITTO_REGISTRATIONS')) ?? false;
+  },
   /** Proof-of-work configuration. */
   pow: {
     get registrations() {
diff --git a/src/controllers/api/accounts.ts b/src/controllers/api/accounts.ts
index 7ac74a0..1d37f70 100644
--- a/src/controllers/api/accounts.ts
+++ b/src/controllers/api/accounts.ts
@@ -22,6 +22,10 @@ const createAccountSchema = z.object({
 });
 
 const createAccountController: AppController = async (c) => {
+  if (!Conf.registrations) {
+    return c.json({ error: 'Registrations are disabled.' }, 403);
+  }
+
   const pubkey = c.get('pubkey')!;
   const result = createAccountSchema.safeParse(await c.req.json());
 
diff --git a/src/controllers/api/instance.ts b/src/controllers/api/instance.ts
index 8ef38a7..10b359b 100644
--- a/src/controllers/api/instance.ts
+++ b/src/controllers/api/instance.ts
@@ -12,7 +12,7 @@ const instanceController: AppController = (c) => {
     title: 'Ditto',
     description: 'An efficient and flexible social media server.',
     short_description: 'An efficient and flexible social media server.',
-    registrations: false,
+    registrations: Conf.registrations,
     max_toot_chars: Conf.postCharLimit,
     configuration: {
       media_attachments: {