Index: sys/kern/uipc_shm.c
===================================================================
--- sys/kern/uipc_shm.c
+++ sys/kern/uipc_shm.c
@@ -1915,8 +1915,8 @@
 	pi = OFF_TO_IDX(off + PAGE_MASK);
 	error = 0;
 
-	/* Handle the case when offset is beyond shm size */
-	if ((off_t)len < 0) {
+	/* Handle the case when offset is on or beyond shm size */
+	if ((off_t)len <= 0) {
 		*offset = shmfd->shm_size;
 		*length = 0;
 		return (0);