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diff --git a/lib/dns/db.c b/lib/dns/db.c
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index a4c2864..62f461c 100644
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--- a/lib/dns/db.c
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+++ b/lib/dns/db.c
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@@ -860,6 +860,8 @@ dns_db_unregister(dns_dbimplementation_t **dbimp) {
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 	isc_mem_put(mctx, imp, sizeof(dns_dbimplementation_t));
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 	isc_mem_detach(&mctx);
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 	RWUNLOCK(&implock, isc_rwlocktype_write);
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+
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+	*dbimp = NULL;
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 }
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 isc_result_t