diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
index 9d5918eb0a30..3ca35aa4e057 100644
--- a/drivers/md/dm-log-userspace-base.c
+++ b/drivers/md/dm-log-userspace-base.c
@@ -139,6 +139,7 @@ static int build_constructor_string(struct dm_target *ti,
 		str_size += strlen(argv[i]) + 1; /* +1 for space between args */
 
 	str_size += 20; /* Max number of chars in a printed u64 number */
+	str_size++; /* For NUL-terminator */
 
 	str = kzalloc(str_size, GFP_KERNEL);
 	if (!str) {