diff --git a/.config/example.yml b/.config/example.yml
index 3f0ce4031..8e881c187 100644
--- a/.config/example.yml
+++ b/.config/example.yml
@@ -79,8 +79,8 @@ redis:
 #  host: localhost
 #  port: 9200
 #  ssl: false
-#  user: 
-#  pass: 
+#  user:
+#  pass:
 
 #   ┌───────────────┐
 #───┘ ID generation └───────────────────────────────────────────
@@ -109,6 +109,19 @@ id: 'aid'
 # Maximum lenght of an image caption or file comment (default 1500, max 8192)
 #maxCaptionLength: 1500
 
+# Reserved usernames that only the administrator can register with
+reservedUsernames:
+  - root
+  - admin
+  - system
+  - test
+  - proxy
+  - relay
+  - mod
+  - moderator
+  - info
+  - information
+
 # Whether disable HSTS
 #disableHsts: true
 
@@ -211,4 +224,4 @@ id: 'aid'
 # !!!!!!!!!!
 
 # Seriously. Do NOT fill out the above settings if you're self-hosting.
-# They're much better off being set from the control panel. 
+# They're much better off being set from the control panel.
diff --git a/packages/backend/src/config/types.ts b/packages/backend/src/config/types.ts
index a7cdc89cf..4f367debe 100644
--- a/packages/backend/src/config/types.ts
+++ b/packages/backend/src/config/types.ts
@@ -77,6 +77,8 @@ export type Source = {
 		sha256CertFingerprints?: string[];
 	};
 
+	reservedUsernames?: string[];
+
 	// Managed hosting stuff
 	maxUserSignups?: number;
 	isManagedHosting?: boolean;
diff --git a/packages/backend/src/server/api/endpoints/username/available.ts b/packages/backend/src/server/api/endpoints/username/available.ts
index f5aa4ed1e..6fa09ba36 100644
--- a/packages/backend/src/server/api/endpoints/username/available.ts
+++ b/packages/backend/src/server/api/endpoints/username/available.ts
@@ -1,5 +1,6 @@
 import { IsNull } from "typeorm";
 import { Users, UsedUsernames } from "@/models/index.js";
+import config from "@/config/index.js";
 import define from "../../define.js";
 
 export const meta = {
@@ -40,7 +41,11 @@ export default define(meta, paramDef, async (ps) => {
 		username: ps.username.toLowerCase(),
 	});
 
+	const reserved = config.reservedUsernames?.includes(
+		ps.username.toLowerCase(),
+	);
+
 	return {
-		available: exist === 0 && exist2 === 0,
+		available: exist === 0 && exist2 === 0 && !reserved,
 	};
 });
diff --git a/packages/backend/src/server/api/private/signup.ts b/packages/backend/src/server/api/private/signup.ts
index 754d86c3b..d24a74c12 100644
--- a/packages/backend/src/server/api/private/signup.ts
+++ b/packages/backend/src/server/api/private/signup.ts
@@ -44,6 +44,11 @@ export default async (ctx: Koa.Context) => {
 	const invitationCode = body["invitationCode"];
 	const emailAddress = body["emailAddress"];
 
+	if (config.reservedUsernames?.includes(username.toLowerCase())) {
+		ctx.status = 400;
+		return;
+	}
+
 	if (instance.emailRequiredForSignup) {
 		if (emailAddress == null || typeof emailAddress !== "string") {
 			ctx.status = 400;