diff --git a/src/librbd/io/SimpleSchedulerObjectDispatch.cc b/src/librbd/io/SimpleSchedulerObjectDispatch.cc
index 6b50c46ad52..cd2ffb1975d 100644
--- a/src/librbd/io/SimpleSchedulerObjectDispatch.cc
+++ b/src/librbd/io/SimpleSchedulerObjectDispatch.cc
@@ -105,7 +105,8 @@ bool SimpleSchedulerObjectDispatch<I>::ObjectRequests::try_delay_request(
 
     // try to merge back to an existing request
     iter = m_delayed_requests.lower_bound(object_off);
-    if (iter == m_delayed_requests.end() || iter->first > object_off) {
+    if (iter != m_delayed_requests.begin() &&
+        (iter == m_delayed_requests.end() || iter->first > object_off)) {
       iter--;
     }
     if (iter != m_delayed_requests.end() &&