diff --git a/src/tls/asn1.c b/src/tls/asn1.c
index ee9a3afdf..970f680c1 100644
--- a/src/tls/asn1.c
+++ b/src/tls/asn1.c
@@ -129,6 +129,8 @@ static int asn1_valid_der(struct asn1_hdr *hdr)
 		return 1;
 	if (hdr->tag == ASN1_TAG_BOOLEAN && !asn1_valid_der_boolean(hdr))
 		return 0;
+	if (hdr->tag == ASN1_TAG_NULL && hdr->length != 0)
+		return 0;
 	return 1;
 }