diff --git a/src/voice/gevActions.js b/src/voice/gevActions.js
index 20a502a82..f7860749f 100644
--- a/src/voice/gevActions.js
+++ b/src/voice/gevActions.js
@@ -332,7 +332,9 @@ function unavailableOnEngine(
     engine: engine?.kind ?? null,
     feature: what,
     suggestion: SWITCH_ENGINE_HINT,
-    error: `${what} is not available on ${engineName(engine)} yet. Switch to the Cesium engine (${SWITCH_ENGINE_HINT}) to use it.`,
+    error: /\blayers$/.test(what)
+      ? `${what} are not available on ${engineName(engine)} yet. Switch to the Cesium engine (${SWITCH_ENGINE_HINT}) to use them.`
+      : `${what} is not available on ${engineName(engine)} yet. Switch to the Cesium engine (${SWITCH_ENGINE_HINT}) to use it.`,
   };
 }
 
@@ -1110,6 +1112,29 @@ export function createGevActionRunner({
     }
 
     if (name === 'analyst_query') {
+      // Layers this engine's catalog left out cannot be asked: say so rather
+      // than answer zero.
+      const missing = !viewer
+        ? (Array.isArray(args.layers) ? args.layers : [])
+            .map(normalizeLayerId)
+            .filter(
+              (layerId) =>
+                layerId &&
+                voiceLayer(layerId) &&
+                !dataManager.layers.has(layerId),
+            )
+        : [];
+      if (missing.length)
+        return {
+          ...unavailableOnEngine(
+            'analyst_query',
+            engine,
+            missing.length === 1
+              ? `The ${missing[0]} layer`
+              : `The ${missing.join(', ')} layers`,
+          ),
+          layerIds: missing,
+        };
       return runAnalystQuery(
         ensureAnalystEngine(),
         dataManager,
@@ -2484,6 +2509,8 @@ function stopAllTracking(engine, dataManager) {
     ['military', 'selectedMilitaryTrackingId'],
     ['satellites', 'selectedSatTrackingId'],
   ]) {
+    // A layer this engine does not have tracks nothing to clear.
+    if (dataManager.layers && !dataManager.layers.has(layerId)) continue;
     try {
       if (
         dataManager.setLayerParams(
diff --git a/src/voice/gevActionsEngine.test.mjs b/src/voice/gevActionsEngine.test.mjs
index 7506fee0c..68e2965ad 100644
--- a/src/voice/gevActionsEngine.test.mjs
+++ b/src/voice/gevActionsEngine.test.mjs
@@ -504,3 +504,54 @@ test('without a viewer a layer the engine lacks refuses instead of throwing', as
     'a name no engine knows is still an unknown layer',
   );
 });
+
+test('without a viewer analyst_query on a layer the engine lacks refuses', async () => {
+  const engine = engineOverAustin({ kind: 'navara' });
+  const runner = runnerOn(engine, {
+    dataManager: dataManagerWith({ flights: {} }),
+  });
+  const one = await runner('analyst_query', { layers: ['cctv'] });
+  assert.equal(one.ok, false);
+  assert.equal(one.code, UNAVAILABLE_ON_ENGINE);
+  assert.deepEqual(one.layerIds, ['cctv']);
+  assert.match(
+    one.error,
+    /^The cctv layer is not available on the Navara engine yet/,
+  );
+  const two = await runner('analyst_query', { layers: ['cctv', 'vessels'] });
+  assert.match(
+    two.error,
+    /^The cctv, ais-live-vessels layers are not available on the Navara engine yet\. Switch to the Cesium engine \(\?engine=cesium\) to use them\.$/,
+  );
+});
+
+test('stop_tracking with nothing tracked is a no-op success, also without the layers', async () => {
+  const engine = engineOverAustin({ kind: 'navara' });
+  const dataManager = dataManagerWith({
+    flights: { getTrackedInfo: () => null },
+  });
+  // As the manager answers: a layer it does not hold takes no params.
+  dataManager.setLayerParams = (id) => dataManager.layers.has(id);
+  const runner = runnerOn(engine, { dataManager });
+  const result = await runner('stop_tracking', {});
+  assert.equal(result.ok, true);
+  assert.deepEqual(result.released, []);
+});
+
+test('the spoken refusal of an unavailable layer carries its reason', async () => {
+  const { SPEECH_BUILDERS } = await import('./speech.js');
+  const engine = engineOverAustin({ kind: 'navara' });
+  const runner = runnerOn(engine, {
+    dataManager: dataManagerWith({ flights: {} }),
+  });
+  const result = await runner('set_layer_visibility', {
+    layerId: 'cctv',
+    enabled: true,
+  });
+  const speech = SPEECH_BUILDERS.set_layer_visibility(result, {
+    layerId: 'cctv',
+    enabled: true,
+  });
+  assert.equal(speech.say, result.error);
+  assert.match(speech.say, /Switch to the Cesium engine/);
+});
diff --git a/src/voice/speech.js b/src/voice/speech.js
index 31716e03e..8d5f15bf3 100644
--- a/src/voice/speech.js
+++ b/src/voice/speech.js
@@ -103,6 +103,13 @@ function setLayerVisibility(result, args = {}) {
   if (result?.cancelled) return null;
   if (!result?.ok) {
     const wanted = args.enabled === false ? 'off' : 'on';
+    // An engine without the layer says why and what to do (the refusal's
+    // own sentence), not only that it failed.
+    if (result?.code === 'UNAVAILABLE_ON_ENGINE' && result.error)
+      return {
+        say: result.error,
+        display: { title: label, lines: [result.error] },
+      };
     return {
       say: `Couldn't turn ${wanted} ${label}.`,
       display: { title: label, lines: [result?.error].filter(Boolean) },