diff --git a/swapon.c b/swapon.c
index 0610385..278aa73 100644
--- a/swapon.c
+++ b/swapon.c
@@ -10,7 +10,7 @@
 static void
 usage(void)
 {
-	eprintf("usage: %s [-d] [-a] device\n", argv0);
+	eprintf("usage: %s [-dp] [-a] device\n", argv0);
 }
 
 int
@@ -28,6 +28,9 @@ main(int argc, char *argv[])
 	case 'd':
 		flags |= SWAP_FLAG_DISCARD;
 		break;
+	case 'p':
+		flags |= SWAP_FLAG_PREFER;
+		break;
 	default:
 		usage();
 	} ARGEND;