diff --git a/ext/bg/js/anki-note-builder.js b/ext/bg/js/anki-note-builder.js
index 700d8237..9bab095d 100644
--- a/ext/bg/js/anki-note-builder.js
+++ b/ext/bg/js/anki-note-builder.js
@@ -85,14 +85,14 @@ class AnkiNoteBuilder {
         });
     }
 
-    async injectAudio(definition, fields, sources, optionsContext) {
+    async injectAudio(definition, fields, sources, details) {
         if (!this._containsMarker(fields, 'audio')) { return; }
 
         try {
             const expressions = definition.expressions;
             const audioSourceDefinition = Array.isArray(expressions) ? expressions[0] : definition;
 
-            const {uri} = await this._audioSystem.getDefinitionAudio(audioSourceDefinition, sources, {tts: false, optionsContext});
+            const {uri} = await this._audioSystem.getDefinitionAudio(audioSourceDefinition, sources, details);
             const filename = this._createInjectedAudioFileName(audioSourceDefinition);
             if (filename !== null) {
                 definition.audio = {url: uri, filename};
diff --git a/ext/bg/js/audio-uri-builder.js b/ext/bg/js/audio-uri-builder.js
index dfd195d8..27e97680 100644
--- a/ext/bg/js/audio-uri-builder.js
+++ b/ext/bg/js/audio-uri-builder.js
@@ -49,11 +49,11 @@ class AudioUriBuilder {
         return url;
     }
 
-    async getUri(definition, source, options) {
+    async getUri(definition, source, details) {
         const handler = this._getUrlHandlers.get(source);
         if (typeof handler === 'function') {
             try {
-                return await handler(definition, options);
+                return await handler(definition, details);
             } catch (e) {
                 // NOP
             }
@@ -132,26 +132,24 @@ class AudioUriBuilder {
         throw new Error('Failed to find audio URL');
     }
 
-    async _getUriTextToSpeech(definition, options) {
-        const voiceURI = options.audio.textToSpeechVoice;
-        if (!voiceURI) {
+    async _getUriTextToSpeech(definition, {textToSpeechVoice}) {
+        if (!textToSpeechVoice) {
             throw new Error('No voice');
         }
-
-        return `tts:?text=${encodeURIComponent(definition.expression)}&voice=${encodeURIComponent(voiceURI)}`;
+        return `tts:?text=${encodeURIComponent(definition.expression)}&voice=${encodeURIComponent(textToSpeechVoice)}`;
     }
 
-    async _getUriTextToSpeechReading(definition, options) {
-        const voiceURI = options.audio.textToSpeechVoice;
-        if (!voiceURI) {
+    async _getUriTextToSpeechReading(definition, {textToSpeechVoice}) {
+        if (!textToSpeechVoice) {
             throw new Error('No voice');
         }
-
-        return `tts:?text=${encodeURIComponent(definition.reading || definition.expression)}&voice=${encodeURIComponent(voiceURI)}`;
+        return `tts:?text=${encodeURIComponent(definition.reading || definition.expression)}&voice=${encodeURIComponent(textToSpeechVoice)}`;
     }
 
-    async _getUriCustom(definition, options) {
-        const customSourceUrl = options.audio.customSourceUrl;
+    async _getUriCustom(definition, {customSourceUrl}) {
+        if (typeof customSourceUrl !== 'string') {
+            throw new Error('No custom URL defined');
+        }
         return customSourceUrl.replace(/\{([^}]*)\}/g, (m0, m1) => (hasOwn(definition, m1) ? `${definition[m1]}` : m0));
     }
 }
diff --git a/ext/bg/js/backend.js b/ext/bg/js/backend.js
index a1b788df..79402e67 100644
--- a/ext/bg/js/backend.js
+++ b/ext/bg/js/backend.js
@@ -51,8 +51,10 @@ class Backend {
         this.options = null;
         this.optionsSchema = null;
         this.defaultAnkiFieldTemplates = null;
-        this.audioSystem = new AudioSystem({getAudioUri: this._getAudioUri.bind(this)});
         this.audioUriBuilder = new AudioUriBuilder();
+        this.audioSystem = new AudioSystem({
+            audioUriBuilder: this.audioUriBuilder
+        });
         this.ankiNoteBuilder = new AnkiNoteBuilder({
             anki: this.anki,
             audioSystem: this.audioSystem,
@@ -494,11 +496,12 @@ class Backend {
         const templates = this.defaultAnkiFieldTemplates;
 
         if (mode !== 'kanji') {
+            const {customSourceUrl} = options.audio;
             await this.ankiNoteBuilder.injectAudio(
                 definition,
                 options.anki.terms.fields,
                 options.audio.sources,
-                optionsContext
+                {textToSpeechVoice: null, customSourceUrl}
             );
         }
 
@@ -573,9 +576,8 @@ class Backend {
         return this._runCommand(command, params);
     }
 
-    async _onApiAudioGetUri({definition, source, optionsContext}) {
-        const options = this.getOptions(optionsContext);
-        return await this.audioUriBuilder.getUri(definition, source, options);
+    async _onApiAudioGetUri({definition, source, details}) {
+        return await this.audioUriBuilder.getUri(definition, source, details);
     }
 
     _onApiScreenshotGet({options}, sender) {
@@ -861,16 +863,6 @@ class Backend {
         }
     }
 
-    async _getAudioUri(definition, source, details) {
-        let optionsContext = (typeof details === 'object' && details !== null ? details.optionsContext : null);
-        if (!(typeof optionsContext === 'object' && optionsContext !== null)) {
-            optionsContext = this.optionsContext;
-        }
-
-        const options = this.getOptions(optionsContext);
-        return await this.audioUriBuilder.getUri(definition, source, options);
-    }
-
     async _renderTemplate(template, data) {
         return handlebarsRenderDynamic(template, data);
     }
diff --git a/ext/bg/js/settings/audio.js b/ext/bg/js/settings/audio.js
index 3c6e126c..e9aa72e1 100644
--- a/ext/bg/js/settings/audio.js
+++ b/ext/bg/js/settings/audio.js
@@ -28,12 +28,7 @@ let audioSourceUI = null;
 let audioSystem = null;
 
 async function audioSettingsInitialize() {
-    audioSystem = new AudioSystem({
-        getAudioUri: async (definition, source) => {
-            const optionsContext = getOptionsContext();
-            return await apiAudioGetUri(definition, source, optionsContext);
-        }
-    });
+    audioSystem = new AudioSystem({audioUriBuilder: null});
 
     const optionsContext = getOptionsContext();
     const options = await getOptionsMutable(optionsContext);
diff --git a/ext/mixed/js/api.js b/ext/mixed/js/api.js
index 7080d93a..c97dc687 100644
--- a/ext/mixed/js/api.js
+++ b/ext/mixed/js/api.js
@@ -64,8 +64,8 @@ function apiTemplateRender(template, data) {
     return _apiInvoke('templateRender', {data, template});
 }
 
-function apiAudioGetUri(definition, source, optionsContext) {
-    return _apiInvoke('audioGetUri', {definition, source, optionsContext});
+function apiAudioGetUri(definition, source, details) {
+    return _apiInvoke('audioGetUri', {definition, source, details});
 }
 
 function apiCommandExec(command, params) {
diff --git a/ext/mixed/js/audio-system.js b/ext/mixed/js/audio-system.js
index 45b733fc..574ad3dc 100644
--- a/ext/mixed/js/audio-system.js
+++ b/ext/mixed/js/audio-system.js
@@ -66,10 +66,10 @@ class TextToSpeechAudio {
 }
 
 class AudioSystem {
-    constructor({getAudioUri}) {
+    constructor({audioUriBuilder}) {
         this._cache = new Map();
         this._cacheSizeMaximum = 32;
-        this._getAudioUri = getAudioUri;
+        this._audioUriBuilder = audioUriBuilder;
 
         if (typeof speechSynthesis !== 'undefined') {
             // speechSynthesis.getVoices() will not be populated unless some API call is made.
@@ -90,7 +90,7 @@ class AudioSystem {
             if (uri === null) { continue; }
 
             try {
-                const audio = await this._createAudio(uri, details);
+                const audio = await this._createAudio(uri);
                 this._cacheCheck();
                 this._cache.set(key, {audio, uri, source});
                 return {audio, uri, source};
@@ -114,20 +114,23 @@ class AudioSystem {
         // NOP
     }
 
-    async _createAudio(uri, details) {
+    async _createAudio(uri) {
         const ttsParameters = this._getTextToSpeechParameters(uri);
         if (ttsParameters !== null) {
-            if (typeof details === 'object' && details !== null) {
-                if (details.tts === false) {
-                    throw new Error('Text-to-speech not permitted');
-                }
-            }
             return this.createTextToSpeechAudio(ttsParameters);
         }
 
         return await this._createAudioFromUrl(uri);
     }
 
+    _getAudioUri(definition, source, details) {
+        return (
+            this._audioUriBuilder !== null ?
+            this._audioUriBuilder.getUri(definition, source, details) :
+            null
+        );
+    }
+
     _createAudioFromUrl(url) {
         return new Promise((resolve, reject) => {
             const audio = new Audio(url);
diff --git a/ext/mixed/js/display.js b/ext/mixed/js/display.js
index 63687dc2..7f3ba859 100644
--- a/ext/mixed/js/display.js
+++ b/ext/mixed/js/display.js
@@ -45,7 +45,13 @@ class Display {
         this.index = 0;
         this.audioPlaying = null;
         this.audioFallback = null;
-        this.audioSystem = new AudioSystem({getAudioUri: this._getAudioUri.bind(this)});
+        this.audioSystem = new AudioSystem({
+            audioUriBuilder: {
+                async getUri(definition, source, details) {
+                    return await apiAudioGetUri(definition, source, details);
+                }
+            }
+        });
         this.styleNode = null;
 
         this.eventListeners = new EventListenerCollection();
@@ -789,10 +795,10 @@ class Display {
                 this.audioPlaying = null;
             }
 
-            const sources = this.options.audio.sources;
             let audio, source, info;
             try {
-                ({audio, source} = await this.audioSystem.getDefinitionAudio(expression, sources));
+                const {sources, textToSpeechVoice, customSourceUrl} = this.options.audio;
+                ({audio, source} = await this.audioSystem.getDefinitionAudio(expression, sources, {textToSpeechVoice, customSourceUrl}));
                 info = `From source ${1 + sources.indexOf(source)}: ${source}`;
             } catch (e) {
                 if (this.audioFallback === null) {
@@ -947,9 +953,4 @@ class Display {
             }
         };
     }
-
-    async _getAudioUri(definition, source) {
-        const optionsContext = this.getOptionsContext();
-        return await apiAudioGetUri(definition, source, optionsContext);
-    }
 }