diff --git a/src/lib/shared/tts-provider-catalog.ts b/src/lib/shared/tts-provider-catalog.ts
index 86c1466..cb30fc2 100644
--- a/src/lib/shared/tts-provider-catalog.ts
+++ b/src/lib/shared/tts-provider-catalog.ts
@@ -232,7 +232,9 @@ export function getDefaultVoices(provider: TtsProviderId, model: string): string
   }
 
   if (provider === 'custom-openai') {
-    return isKokoroModel(model) ? [...KOKORO_DEFAULT_VOICES] : [...CUSTOM_OPENAI_DEFAULT_VOICES];
+    // Kokoro models get the kokoro voice set; any other OpenAI-compatible model
+    // falls back to the canonical OpenAI six, which such servers generally accept.
+    return isKokoroModel(model) ? [...KOKORO_DEFAULT_VOICES] : [...OPENAI_DEFAULT_VOICES];
   }
 
   if (provider === 'replicate') {
diff --git a/tests/unit/tts-provider-catalog.vitest.spec.ts b/tests/unit/tts-provider-catalog.vitest.spec.ts
index 02e72af..3453cc1 100644
--- a/tests/unit/tts-provider-catalog.vitest.spec.ts
+++ b/tests/unit/tts-provider-catalog.vitest.spec.ts
@@ -41,6 +41,8 @@ describe('tts provider catalog', () => {
   test('resolves default voices and instruction support unchanged', () => {
     expect(getDefaultVoices('openai', 'gpt-4o-mini-tts')).toContain('sage');
     expect(getDefaultVoices('custom-openai', 'kokoro')).toContain('af_sarah');
+    // Non-kokoro custom-openai models fall back to the canonical OpenAI six.
+    expect(getDefaultVoices('custom-openai', 'supertonic-3')).toEqual(['alloy', 'echo', 'fable', 'onyx', 'nova', 'shimmer']);
     expect(getDefaultVoices('deepinfra', 'ResembleAI/chatterbox')).toEqual(['None']);
     expect(getDefaultVoices('deepinfra', 'Zyphra/Zonos-v0.1-transformer')).toEqual(['random']);
     expect(supportsTtsInstructions('gpt-4o-mini-tts')).toBe(true);