diff --git a/lib/dns/dst_api.c b/lib/dns/dst_api.c
index 237ddc0515..39fcbf1fa6 100644
--- a/lib/dns/dst_api.c
+++ b/lib/dns/dst_api.c
@@ -461,16 +461,22 @@ dst_key_tofile(const dst_key_t *key, int type, const char *directory) {
 
 void
 dst_key_setexternal(dst_key_t *key, bool value) {
+	REQUIRE(VALID_KEY(key));
+
 	key->external = value;
 }
 
 bool
 dst_key_isexternal(dst_key_t *key) {
+	REQUIRE(VALID_KEY(key));
+
 	return (key->external);
 }
 
 void
 dst_key_setmodified(dst_key_t *key, bool value) {
+	REQUIRE(VALID_KEY(key));
+
 	isc_mutex_lock(&key->mdlock);
 	key->modified = value;
 	isc_mutex_unlock(&key->mdlock);
@@ -480,6 +486,8 @@ bool
 dst_key_ismodified(const dst_key_t *key) {
 	bool modified;
 
+	REQUIRE(VALID_KEY(key));
+
 	isc_mutex_lock(&(((dst_key_t *)key)->mdlock));
 	modified = key->modified;
 	isc_mutex_unlock(&(((dst_key_t *)key)->mdlock));