diff --git a/lib/dns/diff.c b/lib/dns/diff.c
index a6a78f5d16..3529224558 100644
--- a/lib/dns/diff.c
+++ b/lib/dns/diff.c
@@ -40,7 +40,13 @@
 
 static dns_rdatatype_t
 rdata_covers(dns_rdata_t *rdata) {
-	return rdata->type == dns_rdatatype_rrsig ? dns_rdata_covers(rdata) : 0;
+	if (rdata->type == dns_rdatatype_rrsig ||
+	    rdata->type == dns_rdatatype_sig)
+	{
+		return dns_rdata_covers(rdata);
+	}
+
+	return 0;
 }
 
 isc_result_t