diff --git a/src/p2pool.cpp b/src/p2pool.cpp
index aa26af4..2800dc9 100644
--- a/src/p2pool.cpp
+++ b/src/p2pool.cpp
@@ -588,7 +588,7 @@ void p2pool::submit_block_async(std::vector<uint8_t>&& blob)
 	}
 }
 
-void p2pool::submit_aux_block(const hash& chain_id, uint32_t template_id, uint32_t nonce, uint32_t extra_nonce)
+void p2pool::submit_aux_block(const hash& chain_id, uint32_t template_id, uint32_t nonce, uint32_t extra_nonce) const
 {
 	size_t nonce_offset = 0;
 	size_t extra_nonce_offset = 0;
diff --git a/src/p2pool.h b/src/p2pool.h
index 0d18624..09abffb 100644
--- a/src/p2pool.h
+++ b/src/p2pool.h
@@ -87,7 +87,7 @@ public:
 	void submit_block_async(uint32_t template_id, uint32_t nonce, uint32_t extra_nonce);
 	void submit_block_async(std::vector<uint8_t>&& blob);
 
-	void submit_aux_block(const hash& chain_id, uint32_t template_id, uint32_t nonce, uint32_t extra_nonce);
+	void submit_aux_block(const hash& chain_id, uint32_t template_id, uint32_t nonce, uint32_t extra_nonce) const;
 
 	bool submit_sidechain_block(uint32_t template_id, uint32_t nonce, uint32_t extra_nonce);
 
diff --git a/tests/src/merkle_tests.cpp b/tests/src/merkle_tests.cpp
index 420325c..2fe3915 100644
--- a/tests/src/merkle_tests.cpp
+++ b/tests/src/merkle_tests.cpp
@@ -281,12 +281,28 @@ TEST(merkle, params)
 	ASSERT_EQ(PoolBlock::encode_merkle_tree_data(127, 0), 0x3F6U);
 	ASSERT_EQ(PoolBlock::encode_merkle_tree_data(127, 0xFFFFFFFFU), 0x3FFFFFFFFF6ULL);
 
+	PoolBlock b;
+	uint32_t n1, nonce1;
+
+	b.m_merkleTreeData = 0;
+	b.decode_merkle_tree_data(n1, nonce1);
+	ASSERT_TRUE(n1 == 1 && nonce1 == 0);
+
+	b.m_merkleTreeData = 0xFFFFFFFF0ULL;
+	b.decode_merkle_tree_data(n1, nonce1);
+	ASSERT_TRUE(n1 == 1 && nonce1 == 0xFFFFFFFFU);
+
+	b.m_merkleTreeData = 0x3F6U;
+	b.decode_merkle_tree_data(n1, nonce1);
+	ASSERT_TRUE(n1 == 127 && nonce1 == 0);
+
+	b.m_merkleTreeData = 0x3FFFFFFFFF6ULL;
+	b.decode_merkle_tree_data(n1, nonce1);
+	ASSERT_TRUE(n1 == 127 && nonce1 == 0xFFFFFFFFU);
+
 	for (uint32_t n_aux_chains = 1; n_aux_chains < 128; ++n_aux_chains) {
 		for (uint32_t nonce = 1; nonce; nonce <<= 1) {
-			PoolBlock b;
 			b.m_merkleTreeData = PoolBlock::encode_merkle_tree_data(n_aux_chains, nonce);
-
-			uint32_t n1, nonce1;
 			b.decode_merkle_tree_data(n1, nonce1);
 			ASSERT_EQ(n1, n_aux_chains);
 			ASSERT_EQ(nonce1, nonce);