diff --git a/frontend/src/pages/xray/BalancerFormModal.vue b/frontend/src/pages/xray/BalancerFormModal.vue
index 47dd2d41..05aabfeb 100644
--- a/frontend/src/pages/xray/BalancerFormModal.vue
+++ b/frontend/src/pages/xray/BalancerFormModal.vue
@@ -61,6 +61,16 @@ const isValid = computed(
   () => !tagEmpty.value && !duplicateTag.value && !emptySelector.value,
 );
 
+const fallbackSupported = computed(
+  () => form.strategy === 'leastPing' || form.strategy === 'leastLoad',
+);
+
+watch(() => form.strategy, (next) => {
+  if (next !== 'leastPing' && next !== 'leastLoad') {
+    form.fallbackTag = '';
+  }
+});
+
 const tagValidateStatus = computed(() => {
   if (tagEmpty.value) return 'error';
   if (duplicateTag.value) return 'warning';
@@ -111,8 +121,9 @@ const okText = computed(() =>
         </a-select>
       </a-form-item>
 
-      <a-form-item label="Fallback">
-        <a-select v-model:value="form.fallbackTag" allow-clear>
+      <a-form-item label="Fallback"
+        :help="fallbackSupported ? '' : 'Available only with Least ping / Least load'">
+        <a-select v-model:value="form.fallbackTag" allow-clear :disabled="!fallbackSupported">
           <a-select-option v-for="tag in ['', ...outboundTags]" :key="tag || '__empty'" :value="tag">
             {{ tag || `(${t('none')})` }}
           </a-select-option>
diff --git a/frontend/src/pages/xray/BalancersTab.vue b/frontend/src/pages/xray/BalancersTab.vue
index 0cf5b602..255ed108 100644
--- a/frontend/src/pages/xray/BalancersTab.vue
+++ b/frontend/src/pages/xray/BalancersTab.vue
@@ -145,10 +145,11 @@ function syncObservatories() {
 }
 
 function buildWireBalancer(form) {
+  const supportsFallback = form.strategy === 'leastPing' || form.strategy === 'leastLoad';
   const out = {
     tag: form.tag,
     selector: [...form.selector],
-    fallbackTag: form.fallbackTag,
+    fallbackTag: supportsFallback ? form.fallbackTag : '',
   };
   if (form.strategy && form.strategy !== 'random') {
     out.strategy = { type: form.strategy };