# must fail: timed_OS_clock_saturates
# the deadline wraps past the end of u64 (session::FetchSession::tick)
diff --git a/wai/wai-rs/src/http_binding/session.rs b/wai/wai-rs/src/http_binding/session.rs
index ec31518e..d5f96691 100644
--- a/wai/wai-rs/src/http_binding/session.rs
+++ b/wai/wai-rs/src/http_binding/session.rs
@@ -398,7 +398,7 @@ impl FetchSession {
     pub fn tick(&mut self, now_ms: u64) -> Vec<u32> {
         self.now_ms = now_ms;
         let (Some(at), Some(d)) = (self.base_ready_at(), self.policy.refinement_deadline_ms) else { return Vec::new() };
-        if self.result.is_some() || now_ms < at.saturating_add(u64::from(d)) {
+        if self.result.is_some() || now_ms < at.wrapping_add(u64::from(d)) {
             return Vec::new();
         }
         let ids = self.outstanding_of(Class::Refinement);