diff --git a/lib/dns/include/dns/rdata.h b/lib/dns/include/dns/rdata.h
index 7794fb051d..804cd5b76a 100644
--- a/lib/dns/include/dns/rdata.h
+++ b/lib/dns/include/dns/rdata.h
@@ -509,7 +509,7 @@ dns_rdata_tostruct(const dns_rdata_t *rdata, void *target, isc_mem_t *mctx);
  *
  * Requires:
  *
- *\li	'rdata' is a valid, non-empty rdata.
+ *\li	'rdata' is a valid, non-empty, non-pseudo rdata.
  *
  *\li	'target' to point to a valid pointer for the type and class.
  *
diff --git a/lib/dns/rdata.c b/lib/dns/rdata.c
index 3bd7f54661..a255967e46 100644
--- a/lib/dns/rdata.c
+++ b/lib/dns/rdata.c
@@ -1233,6 +1233,7 @@ dns_rdata_tostruct(const dns_rdata_t *rdata, void *target, isc_mem_t *mctx) {
 
 	REQUIRE(rdata != NULL);
 	REQUIRE(DNS_RDATA_VALIDFLAGS(rdata));
+	REQUIRE((rdata->flags & DNS_RDATA_UPDATE) == 0);
 
 	TOSTRUCTSWITCH