diff --git a/lib/dns/cache.c b/lib/dns/cache.c
index 633fc5d122..9935275d8f 100644
--- a/lib/dns/cache.c
+++ b/lib/dns/cache.c
@@ -957,8 +957,9 @@ dns_cache_setcachesize(dns_cache_t *cache, size_t size) {
 		 * time, or replacing other limits).
 		 */
 		isc_mem_setwater(cache->mctx, water, cache, hiwater, lowater);
-		dns_db_adjusthashsize(cache->db, size);
 	}
+
+	dns_db_adjusthashsize(cache->db, size);
 }
 
 size_t
diff --git a/lib/dns/include/dns/db.h b/lib/dns/include/dns/db.h
index 8664cf1458..fe36759a2c 100644
--- a/lib/dns/include/dns/db.h
+++ b/lib/dns/include/dns/db.h
@@ -1400,14 +1400,15 @@ dns_db_hashsize(dns_db_t *db);
 isc_result_t
 dns_db_adjusthashsize(dns_db_t *db, size_t size);
 /*%<
- * For database implementations using a hash table, adjust
- * the size of the hash table to store objects with size
- * memory footprint.
+ * For database implementations using a hash table, adjust the size of
+ * the hash table to store objects with a maximum total memory footprint
+ * of 'size' bytes.  If 'size' is set to 0, it means no finite limit is
+ * requested.
  *
  * Requires:
  *
  * \li	'db' is a valid database.
- * \li  'size' is maximum memory footprint of the database
+ * \li  'size' is maximum memory footprint of the database in bytes
  *
  * Returns:
  * \li	#ISC_R_SUCCESS	The registration succeeded
diff --git a/lib/dns/rbt.c b/lib/dns/rbt.c
index a42b7d08ff..a05fcd8609 100644
--- a/lib/dns/rbt.c
+++ b/lib/dns/rbt.c
@@ -1080,11 +1080,28 @@ isc_result_t
 dns_rbt_adjusthashsize(dns_rbt_t *rbt, size_t size) {
 	REQUIRE(VALID_RBT(rbt));
 
-	size_t newsize = size / RBT_HASH_BUCKETSIZE;
-
-	rbt->maxhashbits = rehash_bits(rbt, newsize);
-
-	maybe_rehash(rbt, newsize);
+	if (size > 0) {
+		/*
+		 * Setting a new, finite size limit was requested for the RBT.
+		 * Estimate how many hash table slots are needed for the
+		 * requested size and how many bits would be needed to index
+		 * those hash table slots, then rehash the RBT if necessary.
+		 * Note that the hash table can only grow, it is not shrunk if
+		 * the requested size limit is lower than the current one.
+		 */
+		size_t newsize = size / RBT_HASH_BUCKETSIZE;
+		rbt->maxhashbits = rehash_bits(rbt, newsize);
+		maybe_rehash(rbt, newsize);
+	} else {
+		/*
+		 * Setting an infinite size limit was requested for the RBT.
+		 * Increase the maximum allowed number of hash table slots to
+		 * 2^32, which enables the hash table to grow as nodes are
+		 * added to the RBT without immediately preallocating 2^32 hash
+		 * table slots.
+		 */
+		rbt->maxhashbits = RBT_HASH_MAX_BITS;
+	}
 
 	return (ISC_R_SUCCESS);
 }