diff --git a/bdk-ffi/src/bdk.udl b/bdk-ffi/src/bdk.udl
index 374ba64..765c997 100644
--- a/bdk-ffi/src/bdk.udl
+++ b/bdk-ffi/src/bdk.udl
@@ -53,9 +53,11 @@ dictionary AddressInfo {
   string address;
 };
 
-enum AddressIndex {
-  "New",
-  "LastUnused",
+[Enum]
+interface AddressIndex {
+  New();
+  LastUnused();
+  Peek(u32 index);
 };
 
 enum Network {
diff --git a/bdk-ffi/src/lib.rs b/bdk-ffi/src/lib.rs
index 21a9db2..7acb254 100644
--- a/bdk-ffi/src/lib.rs
+++ b/bdk-ffi/src/lib.rs
@@ -69,6 +69,9 @@ pub enum AddressIndex {
     /// caller is untrusted; for example when deriving donation addresses on-demand for a public
     /// web page.
     LastUnused,
+    Peek {
+        index: u32,
+    },
 }
 
 impl From<AddressIndex> for BdkAddressIndex {
@@ -76,6 +79,7 @@ impl From<AddressIndex> for BdkAddressIndex {
         match x {
             AddressIndex::New => BdkAddressIndex::New,
             AddressIndex::LastUnused => BdkAddressIndex::LastUnused,
+            AddressIndex::Peek { index } => BdkAddressIndex::Peek(index),
         }
     }
 }