diff --git a/src/client/pages/instance/relays.vue b/src/client/pages/instance/relays.vue
index 568f5edd71..9b523bd0ec 100644
--- a/src/client/pages/instance/relays.vue
+++ b/src/client/pages/instance/relays.vue
@@ -64,6 +64,11 @@ export default Vue.extend({
 				inbox
 			}).then((relay: any) => {
 				this.refresh();
+			}).catch((e: any) => {
+				this.$root.dialog({
+					type: 'error',
+					text: e.message || e
+				});
 			});
 		},
 
@@ -72,6 +77,11 @@ export default Vue.extend({
 				inbox
 			}).then(() => {
 				this.refresh();
+			}).catch((e: any) => {
+				this.$root.dialog({
+					type: 'error',
+					text: e.message || e
+				});
 			});
 		},
 
diff --git a/src/server/api/endpoints/admin/relays/add.ts b/src/server/api/endpoints/admin/relays/add.ts
index 3ea6bcc73b..bcda1050e8 100644
--- a/src/server/api/endpoints/admin/relays/add.ts
+++ b/src/server/api/endpoints/admin/relays/add.ts
@@ -1,6 +1,7 @@
 import $ from 'cafy';
 import define from '../../../define';
 import { addRelay } from '../../../../../services/relay';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -17,8 +18,22 @@ export const meta = {
 			validator: $.str
 		},
 	},
+
+	errors: {
+		invalidUrl: {
+			message: 'Invalid URL',
+			code: 'INVALID_URL',
+			id: 'fb8c92d3-d4e5-44e7-b3d4-800d5cef8b2c'
+		},
+	}
 };
 
 export default define(meta, async (ps, user) => {
+	try {
+		if (new URL(ps.inbox).protocol !== 'https:') throw 'https only';
+	} catch {
+		throw new ApiError(meta.errors.invalidUrl);
+	}
+
 	return await addRelay(ps.inbox);
 });