diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index b414522..79610b5 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -497,7 +497,7 @@
 	}
 
 	error = NULL;
-	size = sizeof(default_buf)/sizeof(default_buf[0]);
+	size = ARRAY_SIZE(default_buf);
 	buf = default_buf;
 
 	while(1){