diff --git a/webui/scripts/test-scheduling-page-structure.mjs b/webui/scripts/test-scheduling-page-structure.mjs
index 3f44d88..c84bc66 100644
--- a/webui/scripts/test-scheduling-page-structure.mjs
+++ b/webui/scripts/test-scheduling-page-structure.mjs
@@ -52,6 +52,7 @@ assert.match(page, /type="email"[\s\S]*aria-label=\{I18N\.participantEmail\}/);
 assert.doesNotMatch(page, /header: I18N\.required|<table|scheduling-table|scheduling-card(?:\s|"|`)/);
 assert.match(page, /aria-label=\{i18nMessage\("i18n:govoplan-scheduling\.decide_on_value/);
 assert.match(page, /submitSchedulingAvailability\(settings, selected\.id/);
+assert.match(page, /option_revision: slot\.revision/);
 assert.match(page, /getSchedulingAvailabilityResponse\(settings, selected\.id\)/);
 assert.match(page, /setAvailability\(Object\.fromEntries\(response\.answers\.map/);
 assert.doesNotMatch(page, /<p>\{selected\.calendar_id\}<\/p>/);
diff --git a/webui/src/api/scheduling.ts b/webui/src/api/scheduling.ts
index fbe90c0..7f2a1ce 100644
--- a/webui/src/api/scheduling.ts
+++ b/webui/src/api/scheduling.ts
@@ -12,6 +12,7 @@ export type SchedulingCandidateSlot = {
   timezone: string;
   location?: string | null;
   position: number;
+  revision: string;
   freebusy_checked_at?: string | null;
   freebusy_status?: string | null;
   freebusy_conflicts: Record<string, unknown>[];
@@ -121,6 +122,7 @@ export type SchedulingAvailabilityPayload = {
   answers: Array<{
     slot_id: string;
     value: SchedulingAvailabilityValue;
+    option_revision: string;
   }>;
 };
 
diff --git a/webui/src/features/scheduling/SchedulingPage.tsx b/webui/src/features/scheduling/SchedulingPage.tsx
index 6620667..50ba6c9 100644
--- a/webui/src/features/scheduling/SchedulingPage.tsx
+++ b/webui/src/features/scheduling/SchedulingPage.tsx
@@ -403,8 +403,16 @@ export default function SchedulingPage({ settings, auth }: { settings: ApiSettin
     event.preventDefault();
     if (!selected || !selectedParticipant || !canRespond || availabilityLoading) return;
     const answers = selected.slots
-      .map((slot) => ({ slot_id: slot.id, value: availability[slot.id] }))
-      .filter((answer): answer is { slot_id: string; value: SchedulingAvailabilityValue } => Boolean(answer.value));
+      .map((slot) => ({
+        slot_id: slot.id,
+        value: availability[slot.id],
+        option_revision: slot.revision
+      }))
+      .filter((answer): answer is {
+        slot_id: string;
+        value: SchedulingAvailabilityValue;
+        option_revision: string;
+      } => Boolean(answer.value));
     if (!answers.length) {
       setError(I18N.selectResponse);
       return;