diff --git a/xen/common/sched/compat.c b/xen/common/sched/compat.c
index d718e450d4..dd97593630 100644
--- a/xen/common/sched/compat.c
+++ b/xen/common/sched/compat.c
@@ -43,9 +43,9 @@ static int compat_poll(struct compat_sched_poll *compat)
 
 #include "core.c"
 
-int compat_set_timer_op(uint32_t lo, int32_t hi)
+int compat_set_timer_op(uint32_t lo, uint32_t hi)
 {
-    return do_set_timer_op(((s64)hi << 32) | lo);
+    return do_set_timer_op(((uint64_t)hi << 32) | lo);
 }
 
 #endif /* __COMMON_SCHED_COMPAT_C__ */
diff --git a/xen/include/hypercall-defs.c b/xen/include/hypercall-defs.c
index 6d361ddfce..47c093acc8 100644
--- a/xen/include/hypercall-defs.c
+++ b/xen/include/hypercall-defs.c
@@ -134,7 +134,7 @@ xenoprof_op(int op, void *arg)
 
 #ifdef CONFIG_COMPAT
 prefix: compat
-set_timer_op(uint32_t lo, int32_t hi)
+set_timer_op(uint32_t lo, uint32_t hi)
 multicall(multicall_entry_compat_t *call_list, uint32_t nr_calls)
 memory_op(unsigned int cmd, void *arg)
 #ifdef CONFIG_IOREQ_SERVER