diff --git a/integrations/chatwoot/src/referral.js b/integrations/chatwoot/src/referral.js
index 9c43ef8..71a0ad9 100644
--- a/integrations/chatwoot/src/referral.js
+++ b/integrations/chatwoot/src/referral.js
@@ -127,8 +127,11 @@ export function mergeMetaWhatsAppReferralAttributes(
   if (options?.consentState !== 'granted') return base;
 
   const candidate = metaWhatsAppReferralAttributes(referral);
-  const hasExistingReferral = Object.keys(base).some(
-    (key) => key.startsWith(META_WHATSAPP_REFERRAL_ATTRIBUTE_PREFIX) && hasValue(base[key]),
+  const hasExistingReferral = META_WHATSAPP_REFERRAL_FIELDS.some(
+    (key) => Object.prototype.hasOwnProperty.call(
+      base,
+      `${META_WHATSAPP_REFERRAL_ATTRIBUTE_PREFIX}${key}`,
+    ),
   );
   if (hasExistingReferral) return base;
 
diff --git a/integrations/chatwoot/tests/referral.test.mjs b/integrations/chatwoot/tests/referral.test.mjs
index 168d115..a8ac912 100644
--- a/integrations/chatwoot/tests/referral.test.mjs
+++ b/integrations/chatwoot/tests/referral.test.mjs
@@ -119,3 +119,11 @@ test('preserves an existing flat referral snapshot without mixing messages', ()
   assert.equal(result.clicktrail_referral_ctwa_clid, undefined);
   assert.equal(result.clicktrail_referral_arbitrary, undefined);
 });
+
+test('treats a recognized flat referral key as occupied regardless of value type', () => {
+  const existing = { clicktrail_referral_source_id: 42 };
+  assert.deepEqual(
+    mergeMetaWhatsAppReferralAttributes(existing, referral, { consentState: 'granted' }),
+    existing,
+  );
+});