diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5dbf8b06d7..5bfd3aa5c0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Changed
  - Repurpose command line gnttab_max_{maptrack_,}frames options so they don't
    cap toolstack provided values.
+ - Ignore VCPUOP_set_singleshot_timer's VCPU_SSHOTTMR_future flag. The only
+   known user doesn't use it properly, leading to in-guest breakage.
 
 ### Added
  - On x86, support for features new in Intel Sapphire Rapids CPUs:
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 626debbae0..6a440590fe 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1762,9 +1762,16 @@ long common_vcpu_op(int cmd, struct vcpu *v, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( copy_from_guest(&set, arg, 1) )
             return -EFAULT;
 
-        if ( (set.flags & VCPU_SSHOTTMR_future) &&
-             (set.timeout_abs_ns < NOW()) )
-            return -ETIME;
+        if ( set.timeout_abs_ns < NOW() )
+        {
+            /*
+             * Simplify the logic if the timeout has already expired and just
+             * inject the event.
+             */
+            stop_timer(&v->singleshot_timer);
+            send_timer_event(v);
+            break;
+        }
 
         migrate_timer(&v->singleshot_timer, smp_processor_id());
         set_timer(&v->singleshot_timer, set.timeout_abs_ns);
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index 81a3b3a743..a836b264a9 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -150,7 +150,10 @@ typedef struct vcpu_set_singleshot_timer vcpu_set_singleshot_timer_t;
 DEFINE_XEN_GUEST_HANDLE(vcpu_set_singleshot_timer_t);
 
 /* Flags to VCPUOP_set_singleshot_timer. */
- /* Require the timeout to be in the future (return -ETIME if it's passed). */
+ /*
+  * Request the timeout to be in the future (return -ETIME if it's passed)
+  * but can be ignored by the hypervisor.
+  */
 #define _VCPU_SSHOTTMR_future (0)
 #define VCPU_SSHOTTMR_future  (1U << _VCPU_SSHOTTMR_future)