diff --git a/sys/src/9/port/segment.c b/sys/src/9/port/segment.c
index 17efff622..2b45af88d 100644
--- a/sys/src/9/port/segment.c
+++ b/sys/src/9/port/segment.c
@@ -610,7 +610,10 @@ segattach(Proc *p, ulong attr, char *name, uintptr va, uintptr len)
 		}
 	}
 
+	/* round up va+len */
+	len += va & (BY2PG-1);
 	len = PGROUND(len);
+
 	if(len == 0)
 		error(Ebadarg);