diff --git a/src/assessment/gateway-assessor.test.ts b/src/assessment/gateway-assessor.test.ts
new file mode 100644
index 0000000..4686556
--- /dev/null
+++ b/src/assessment/gateway-assessor.test.ts
@@ -0,0 +1,38 @@
+/**
+ * AR.IO Observer
+ * Copyright (C) 2022-2026 Permanent Data Solutions, Inc. All Rights Reserved.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+import { expect } from 'chai';
+import * as sinon from 'sinon';
+import * as winston from 'winston';
+
+import { GatewayAssessor } from './gateway-assessor.js';
+
+describe('GatewayAssessor', () => {
+  describe('assessArnsNames', () => {
+    it('leaves out names that are not valid hostname labels', async () => {
+      const referenceGateway = {
+        getArnsResolution: sinon.stub(),
+        checkChunkAvailability: sinon.stub(),
+        getChunkMetadata: sinon.stub(),
+      };
+      const assessor = new GatewayAssessor({
+        referenceGateway,
+        nodeReleaseVersion: 'test-version',
+        nameAssessmentConcurrency: 1,
+        log: winston.createLogger({ silent: true }),
+      });
+
+      // punycode for U+25B6 U+FE0F, rejected by the URL parser
+      const assessments = await assessor.assessArnsNames({
+        host: 'gateway.example.com',
+        names: ['xn--g1h4420f'],
+      });
+
+      expect(assessments).to.deep.equal({});
+      expect(referenceGateway.getArnsResolution.called).to.equal(false);
+    });
+  });
+});
diff --git a/src/assessment/gateway-assessor.ts b/src/assessment/gateway-assessor.ts
index 90e4ef8..e2bd9c6 100644
--- a/src/assessment/gateway-assessor.ts
+++ b/src/assessment/gateway-assessor.ts
@@ -20,6 +20,7 @@ import { Got } from 'got';
 import pMap from 'p-map';
 import { Logger } from 'winston';
 
+import { isAssessableArnsName } from '../lib/arns-validation.js';
 import { createGatewayHttpClient } from '../lib/http-client.js';
 import * as metrics from '../metrics.js';
 import { assessOwnership, getArnsResolution } from '../observer.js';
@@ -200,8 +201,9 @@ export class GatewayAssessor {
     host: string;
     names: string[];
   }): Promise<ArnsNameAssessments> {
+    const assessableNames = names.filter(isAssessableArnsName);
     return pMap(
-      names,
+      assessableNames,
       async (name) => {
         try {
           return await this.assessArnsName({ host, arnsName: name });
@@ -227,7 +229,7 @@ export class GatewayAssessor {
       { concurrency: this.nameAssessmentConcurrency },
     ).then((results) => {
       return results.reduce((assessments, assessment, index) => {
-        assessments[names[index]] = assessment;
+        assessments[assessableNames[index]] = assessment;
         return assessments;
       }, {} as ArnsNameAssessments);
     });
diff --git a/src/config.ts b/src/config.ts
index 09277f9..147b3ca 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -21,6 +21,7 @@ import { fileURLToPath } from 'node:url';
 import yargs from 'yargs';
 import { hideBin } from 'yargs/helpers';
 
+import { isAssessableArnsName } from './lib/arns-validation.js';
 import * as env from './lib/env.js';
 
 export const args = await yargs(hideBin(process.argv))
@@ -115,6 +116,15 @@ export const ARNS_NAMES = parseCommaSeparatedList(
   env.varOrDefault('ARNS_NAMES', args.arnsNames ?? ''),
 );
 
+const invalidArnsNames = ARNS_NAMES.filter(
+  (name) => !isAssessableArnsName(name),
+);
+if (invalidArnsNames.length > 0) {
+  throw new Error(
+    `Invalid configuration: ARNS_NAMES contains names that are not valid hostname labels: ${invalidArnsNames.join(', ')}.`,
+  );
+}
+
 // Whitepaper v3.0.0 §10.3: "eight (8) 'chosen names' selected
 // independently by each observer". The default lived at `1` since the
 // constant was introduced in AO days, predating the v3 spec — never
diff --git a/src/lib/arns-validation.ts b/src/lib/arns-validation.ts
index 1bc31e3..faed3a2 100644
--- a/src/lib/arns-validation.ts
+++ b/src/lib/arns-validation.ts
@@ -18,6 +18,13 @@
 
 import { ArnsResolution } from '../types.js';
 
+// Registered names can still be invalid hostname labels (xn--g1h4420f is
+// punycode for U+25B6 U+FE0F, which IDNA rejects). No gateway can be reached
+// under such a name, so it can't be used for assessment.
+export function isAssessableArnsName(name: string): boolean {
+  return URL.canParse(`https://${name}.invalid/`);
+}
+
 export function validateArnsResolutionHeaders(
   resolution: ArnsResolution,
   source: string,
diff --git a/src/names/solana-names-source.test.ts b/src/names/solana-names-source.test.ts
index 5dba663..c509abc 100644
--- a/src/names/solana-names-source.test.ts
+++ b/src/names/solana-names-source.test.ts
@@ -158,6 +158,20 @@ describe('SolanaNamesSource', () => {
       const names = await src.getAllNames(0);
       expect(names).to.deep.equal(['also-real', 'real']);
     });
+
+    it('skips names that are not valid hostname labels', async () => {
+      const stub = sinon.stub().resolves({
+        // xn--g1h4420f is punycode for U+25B6 U+FE0F, rejected by URL
+        items: [{ name: 'real' }, { name: 'xn--g1h4420f' }],
+        nextCursor: undefined,
+      });
+      // only getArNSRecords is used by getAllNames
+      const readable = {
+        getArNSRecords: stub,
+      } as unknown as SolanaARIOReadable;
+      const src = new SolanaNamesSource({ readable, log: makeLog() });
+      expect(await src.getAllNames(0)).to.deep.equal(['real']);
+    });
   });
 
   describe('convenience methods', () => {
diff --git a/src/names/solana-names-source.ts b/src/names/solana-names-source.ts
index ab1968f..6b1823b 100644
--- a/src/names/solana-names-source.ts
+++ b/src/names/solana-names-source.ts
@@ -22,6 +22,7 @@
 import type winston from 'winston';
 
 import type { SolanaARIOReadable } from '@ar.io/sdk';
+import { isAssessableArnsName } from '../lib/arns-validation.js';
 import type { ArnsNameList, ArnsNamesSource } from '../types.js';
 
 export interface SolanaNamesSourceConfig {
@@ -98,7 +99,10 @@ export class SolanaNamesSource implements ArnsNamesSource, ArnsNameList {
         limit: this.pageSize,
       });
       for (const record of page.items) {
-        if (record.name) seen.add(record.name);
+        // Unusable names stay out so the chosen-name sampler picks another.
+        if (record.name && isAssessableArnsName(record.name)) {
+          seen.add(record.name);
+        }
       }
       cursor = page.nextCursor;
       pages += 1;
diff --git a/src/observer.test.ts b/src/observer.test.ts
index 56b454c..a9d5033 100644
--- a/src/observer.test.ts
+++ b/src/observer.test.ts
@@ -492,6 +492,20 @@ describe('Observer', function () {
       nock.cleanAll();
     });
 
+    describe('assessArnsNames', function () {
+      it('leaves out names that are not valid hostname labels', async function () {
+        // punycode for U+25B6 U+FE0F, rejected by the URL parser
+        const assessments = await observer.assessArnsNames({
+          host: 'gateway.example.com',
+          names: ['xn--g1h4420f'],
+          entropy: Buffer.alloc(32),
+        });
+
+        expect(assessments).to.deep.equal({});
+        expect(referenceGatewayStub.getArnsResolution.called).to.equal(false);
+      });
+    });
+
     describe('calculateFailureRate', function () {
       it('should return 0 for empty report', function () {
         const report: ObserverReport = createReport({
diff --git a/src/observer.ts b/src/observer.ts
index 004061c..f45c13d 100644
--- a/src/observer.ts
+++ b/src/observer.ts
@@ -27,6 +27,7 @@ import {
   selectGatewaysForOffsetAssessment,
 } from './assessment/offset-assessor.js';
 import * as config from './config.js';
+import { isAssessableArnsName } from './lib/arns-validation.js';
 import { customHashPRNG } from './lib/prng.js';
 import log from './log.js';
 import * as metrics from './metrics.js';
@@ -448,8 +449,9 @@ export class Observer {
     names: string[];
     entropy: Buffer;
   }): Promise<ArnsNameAssessments> {
+    const assessableNames = names.filter(isAssessableArnsName);
     return pMap(
-      names,
+      assessableNames,
       async (name) => {
         try {
           return await this.assessArnsName({
@@ -479,7 +481,7 @@ export class Observer {
       { concurrency: this.nameAssessmentConcurrency },
     ).then((results) => {
       return results.reduce((assessments, assessment, index) => {
-        assessments[names[index]] = assessment;
+        assessments[assessableNames[index]] = assessment;
         return assessments;
       }, {} as ArnsNameAssessments);
     });
@@ -626,7 +628,10 @@ export class Observer {
           enforcementEnabled: config.OFFSET_OBSERVATION_ENFORCEMENT_ENABLED,
         });
 
-        const nameCount = new Set([...prescribedNames, ...chosenNames]).size;
+        const nameCount = Object.keys({
+          ...prescribedAssessments,
+          ...chosenAssessments,
+        }).length;
         const namePassCount = Object.values({
           ...prescribedAssessments,
           ...chosenAssessments,