diff --git a/tools/net/ynl/lib/ynl.c b/tools/net/ynl/lib/ynl.c
index ae61ae5b02bf..0871f86c6b66 100644
--- a/tools/net/ynl/lib/ynl.c
+++ b/tools/net/ynl/lib/ynl.c
@@ -368,7 +368,7 @@ int ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr)
 		     "Invalid attribute (binary %s)", policy->name);
 		return -1;
 	case YNL_PT_NUL_STR:
-		if ((!policy->len || len <= policy->len) && !data[len - 1])
+		if (len && (!policy->len || len <= policy->len) && !data[len - 1])
 			break;
 		yerr(yarg->ys, YNL_ERROR_ATTR_INVALID,
 		     "Invalid attribute (string %s)", policy->name);