diff --git a/json/src/lib.rs b/json/src/lib.rs
index 61930614..828f66d7 100644
--- a/json/src/lib.rs
+++ b/json/src/lib.rs
@@ -146,7 +146,7 @@ pub struct GetWalletInfoResult {
     #[serde(rename = "txcount")]
     pub tx_count: usize,
     #[serde(rename = "keypoololdest")]
-    pub keypool_oldest: usize,
+    pub keypool_oldest: Option<usize>,
     #[serde(rename = "keypoolsize")]
     pub keypool_size: usize,
     #[serde(rename = "keypoolsize_hd_internal")]