diff --git a/src/probabilistic/CardinalityCounter.cc b/src/probabilistic/CardinalityCounter.cc
index a256673b79..304bf5151d 100644
--- a/src/probabilistic/CardinalityCounter.cc
+++ b/src/probabilistic/CardinalityCounter.cc
@@ -201,10 +201,10 @@ broker::expected<broker::data> CardinalityCounter::Serialize() const
 	broker::vector v = {m, V, alpha_m};
 	v.reserve(3 + m);
 
-        for ( size_t i = 0; i < m; ++i )
+	for ( size_t i = 0; i < m; ++i )
 		v.emplace_back(static_cast<uint64>(buckets[i]));
 
-        return {v};
+	return {v};
 	}
 
 std::unique_ptr<CardinalityCounter> CardinalityCounter::Unserialize(const broker::data& data)
@@ -219,19 +219,22 @@ std::unique_ptr<CardinalityCounter> CardinalityCounter::Unserialize(const broker
 
 	if ( ! (m && V && alpha_m) )
 		return nullptr;
-
 	if ( v->size() != 3 + *m )
 		return nullptr;
 
 	auto cc = std::unique_ptr<CardinalityCounter>(new CardinalityCounter(*m, *V, *alpha_m));
+	if ( *m != cc->m )
+		return nullptr;
+	if ( cc->buckets.size() != * m )
+		return nullptr;
 
-        for ( size_t i = 0; i < *m; ++i )
+	for ( size_t i = 0; i < *m; ++i )
 		{
 		auto x = caf::get_if<uint64>(&(*v)[3 + i]);
 		if ( ! x )
 			return nullptr;
 
-		cc->buckets.push_back(*x);
+		cc->buckets[i] = *x;
 		}
 
 	return cc;
diff --git a/src/probabilistic/cardinality-counter.bif b/src/probabilistic/cardinality-counter.bif
index 2fa7953c9e..1e12765b57 100644
--- a/src/probabilistic/cardinality-counter.bif
+++ b/src/probabilistic/cardinality-counter.bif
@@ -90,7 +90,7 @@ function hll_cardinality_merge_into%(handle1: opaque of cardinality, handle2: op
 	bool res = h1->Merge(h2);
 	if ( ! res )
 		{
-		reporter->Error("Carinality counters with different parameters cannot be merged");
+		reporter->Error("Cardinality counters with different parameters cannot be merged");
 		return val_mgr->GetBool(0);
 		}
 
diff --git a/testing/btest/Baseline/broker.opaque/out b/testing/btest/Baseline/broker.opaque/out
index f35f4e3284..4582e8dc2b 100644
--- a/testing/btest/Baseline/broker.opaque/out
+++ b/testing/btest/Baseline/broker.opaque/out
@@ -4,6 +4,7 @@
 ============ HLL
 3.000069
 3.000069
+3.000069
 ============ Bloom
 0
 1
diff --git a/testing/btest/Baseline/language.copy-all-opaques/out b/testing/btest/Baseline/language.copy-all-opaques/out
index ad38ca1a8d..68b12cecac 100644
--- a/testing/btest/Baseline/language.copy-all-opaques/out
+++ b/testing/btest/Baseline/language.copy-all-opaques/out
@@ -4,6 +4,7 @@
 ============ HLL
 3.000069
 3.000069
+3.000069
 ============ Bloom
 0
 1
diff --git a/testing/btest/broker/opaque.zeek b/testing/btest/broker/opaque.zeek
index f65fc191dd..bddd68e0be 100644
--- a/testing/btest/broker/opaque.zeek
+++ b/testing/btest/broker/opaque.zeek
@@ -26,6 +26,10 @@ event zeek_init()
 	hll_cardinality_add(c1, 2004);
 	print hll_cardinality_estimate(c2);
 
+	local c3 = hll_cardinality_init(0.01, 0.95);
+	hll_cardinality_merge_into(c3, c2);
+	print hll_cardinality_estimate(c3);
+
 	print "============ Bloom";
 	local bf_cnt = bloomfilter_basic_init(0.1, 1000);
 	bloomfilter_add(bf_cnt, 42);
diff --git a/testing/btest/language/copy-all-opaques.zeek b/testing/btest/language/copy-all-opaques.zeek
index 25ca89fd80..06b4a07471 100644
--- a/testing/btest/language/copy-all-opaques.zeek
+++ b/testing/btest/language/copy-all-opaques.zeek
@@ -27,6 +27,10 @@ event zeek_init()
 	hll_cardinality_add(c1, 2004);
 	print hll_cardinality_estimate(c2);
 
+	local c3 = hll_cardinality_init(0.01, 0.95);
+	hll_cardinality_merge_into(c3, c2);
+	print hll_cardinality_estimate(c3);
+
 	print "============ Bloom";
 	local bf_cnt = bloomfilter_basic_init(0.1, 1000);
 	bloomfilter_add(bf_cnt, 42);