diff --git a/crates/ruma-client-api/src/receipt/create_receipt.rs b/crates/ruma-client-api/src/receipt/create_receipt.rs
index 65b89f71..15e41766 100644
--- a/crates/ruma-client-api/src/receipt/create_receipt.rs
+++ b/crates/ruma-client-api/src/receipt/create_receipt.rs
@@ -45,7 +45,7 @@ pub mod v3 {
             /// [`ReceiptType::FullyRead`].
             ///
             /// Defaults to [`ReceiptThread::Unthreaded`].
-            #[serde(rename = "thread_id", skip_serializing_if = "ruma_common::serde::is_default")]
+            #[serde(rename = "thread_id", default, skip_serializing_if = "ruma_common::serde::is_default")]
             pub thread: ReceiptThread,
         }