diff --git a/data_device.c b/data_device.c
index 544b937..f86a9b2 100644
--- a/data_device.c
+++ b/data_device.c
@@ -1005,7 +1005,11 @@ SetSelection (struct wl_client *client, struct wl_resource *resource,
 	     client, wl_resource_get_id (source_resource), serial);
 #endif
 
-  if (serial < last_selection_change_serial)
+  /* Note that both serial and last_selection_change_serial are
+     unsigned.  Remember two's complement arithmetic.  -1 is
+     0xffffffff, while -4294967295 overflows twice and is
+     0x00000001.  */
+  if (serial - last_selection_change_serial > UINT32_MAX / 2)
     {
 #ifdef DEBUG
       fprintf (stderr, "wl_client@%p could not set the selection, "
diff --git a/primary_selection.c b/primary_selection.c
index 70429c8..5177fd0 100644
--- a/primary_selection.c
+++ b/primary_selection.c
@@ -512,7 +512,9 @@ SetSelection (struct wl_client *client, struct wl_resource *resource,
     /* This device is inert, since the seat has been deleted.  */
     return;
 
-  if (serial < last_change_serial)
+  /* Note that both serial and last_change_serial are unsigned.
+     Remember two's complement arithmetic.  */
+  if (serial - last_change_serial > UINT32_MAX / 2)
     /* This change is out of date.  Do nothing.  */
     return;