diff --git a/lib/compute-at-edge-abi/compute-at-edge.witx b/lib/compute-at-edge-abi/compute-at-edge.witx
index be0cbf06..baddeed2 100644
--- a/lib/compute-at-edge-abi/compute-at-edge.witx
+++ b/lib/compute-at-edge-abi/compute-at-edge.witx
@@ -107,6 +107,13 @@
         (result $err (expected $num_bytes (error $fastly_status)))
     )
 
+    (@interface func (export "downstream_client_h2_fingerprint")
+        (param $h2fp_out (@witx pointer (@witx char8)))
+        (param $h2fp_max_len (@witx usize))
+        (param $nwritten_out (@witx pointer (@witx usize)))
+        (result $err (expected (error $fastly_status)))
+    )
+
     (@interface func (export "downstream_client_request_id")
         (param $reqid_out (@witx pointer (@witx char8)))
         (param $reqid_max_len (@witx usize))
diff --git a/lib/src/wiggle_abi/req_impl.rs b/lib/src/wiggle_abi/req_impl.rs
index e730bb6a..bcd51418 100644
--- a/lib/src/wiggle_abi/req_impl.rs
+++ b/lib/src/wiggle_abi/req_impl.rs
@@ -89,6 +89,16 @@ impl FastlyHttpReq for Session {
         }
     }
 
+    #[allow(unused_variables)] // FIXME JDC 2023-06-18: Remove this directive once implemented.
+    fn downstream_client_h2_fingerprint<'a>(
+        &mut self,
+        h2fp_out: &GuestPtr<'a, u8>,
+        h2fp_max_len: u32,
+        nwritten_out: &GuestPtr<u32>,
+    ) -> Result<(), Error> {
+        Err(Error::NotAvailable("Client H2 fingerprint"))
+    }
+
     fn downstream_client_request_id(
         &mut self,
         reqid_out: &GuestPtr<u8>,