diff --git a/server.js b/server.js
index b259d30..8f399c4 100644
--- a/server.js
+++ b/server.js
@@ -135,7 +135,7 @@ app.post("/api/contacts/create", async (req, res) => {
         first_name,
         last_name: last_name || "",
         description: description || "",
-        is_birthdate_known: "false",
+        is_birthdate_known: false,
         is_deceased: false,
         is_deceased_date_known: false
       }),
@@ -281,7 +281,7 @@ export async function writeToMonica(entry) {
           first_name: entry.contact.first_name,
           last_name: entry.contact.last_name || "",
           description: "Automatisch angelegter Kontakt via Friends",
-          is_birthdate_known: entry.contact.birthdate ? (entry.contact.birthdate.startsWith("0000") ? "unknown" : "true") : "false",
+          is_birthdate_known: !!entry.contact.birthdate,
           is_deceased: false,
           is_deceased_date_known: false
         }),
@@ -318,7 +318,7 @@ export async function writeToMonica(entry) {
             first_name: existingData.first_name || entry.contact.first_name || "Unbekannt",
             last_name: existingData.last_name || entry.contact.last_name || "",
             birthdate: entry.contact.birthdate,
-            is_birthdate_known: entry.contact.birthdate.startsWith("0000") ? "unknown" : "true",
+            is_birthdate_known: !!entry.contact.birthdate,
             is_deceased: existingData.is_deceased ?? false,
             is_deceased_date_known: existingData.is_deceased_date_known ?? false
           }),