diff --git a/src/merkle.cpp b/src/merkle.cpp
index 11f800a..4b30c1c 100644
--- a/src/merkle.cpp
+++ b/src/merkle.cpp
@@ -26,6 +26,12 @@ namespace p2pool {
 void merkle_hash(const std::vector<hash>& hashes, root_hash& root)
 {
 	const size_t count = hashes.size();
+
+	if (count == 0) {
+		root.clear();
+		return;
+	}
+
 	const uint8_t* h = hashes[0].h;
 
 	if (count == 1) {
@@ -62,10 +68,15 @@ void merkle_hash(const std::vector<hash>& hashes, root_hash& root)
 void merkle_hash_full_tree(const std::vector<hash>& hashes, std::vector<std::vector<hash>>& tree)
 {
 	const size_t count = hashes.size();
-	const uint8_t* h = hashes[0].h;
 
 	tree.clear();
 
+	if (count == 0) {
+		return;
+	}
+
+	const uint8_t* h = hashes[0].h;
+
 	if (count == 1) {
 		tree.push_back(hashes);
 	}
diff --git a/src/util.h b/src/util.h
index ca5b681..d295834 100644
--- a/src/util.h
+++ b/src/util.h
@@ -175,6 +175,8 @@ template<> FORCEINLINE bool out_of_range<uint64_t>(uint64_t) { return false; }
 template<typename T>
 const uint8_t* readVarint(const uint8_t* data, const uint8_t* data_end, T& b)
 {
+	static_assert(std::is_unsigned_v<T>, "readVarint works only with unsigned types");
+
 	uint64_t result = 0;
 	int k = 0;
 
diff --git a/tests/src/block_template_tests.cpp b/tests/src/block_template_tests.cpp
index 853c8a2..1a67cbc 100644
--- a/tests/src/block_template_tests.cpp
+++ b/tests/src/block_template_tests.cpp
@@ -236,6 +236,7 @@ TEST(block_template, submit_sidechain_block)
 
 	ASSERT_EQ(sidechain.difficulty(), 219467);
 	ASSERT_EQ(sidechain.blocksById().size(), 4487);
+	ASSERT_TRUE(sidechain.precalcFinished());
 
 	const PoolBlock* tip = sidechain.chainTip();
 
diff --git a/tests/src/main.cpp b/tests/src/main.cpp
index 8a240e3..ba79e30 100644
--- a/tests/src/main.cpp
+++ b/tests/src/main.cpp
@@ -28,6 +28,7 @@ using namespace p2pool;
 int main(int argc, char** argv)
 {
 	set_main_thread();
+	p2pool_usage();
 
 	PoolBlock::s_precalculatedSharesLock = new ReadWriteLock();
 
diff --git a/tests/src/merkle_tests.cpp b/tests/src/merkle_tests.cpp
index 87efbde..a9caff0 100644
--- a/tests/src/merkle_tests.cpp
+++ b/tests/src/merkle_tests.cpp
@@ -168,6 +168,17 @@ TEST(merkle, tree)
 		}
 	};
 
+	// 0 leaves
+	uint32_t path_monero;
+	ASSERT_FALSE(tree_path(0, 0, &path_monero));
+
+	merkle_hash(std::vector<hash>(), root);
+	ASSERT_TRUE(root.empty());
+
+	std::vector<std::vector<hash>> tree;
+	merkle_hash_full_tree(std::vector<hash>(), tree);
+	ASSERT_TRUE(tree.empty());
+
 	// 1 leaf
 	merkle_hash(hashes, root);
 	ASSERT_EQ(root, input[0]);
diff --git a/tests/src/util_tests.cpp b/tests/src/util_tests.cpp
index 6977088..389f92b 100644
--- a/tests/src/util_tests.cpp
+++ b/tests/src/util_tests.cpp
@@ -80,6 +80,16 @@ TEST(util, varint)
 	// Invalid value 2
 	uint8_t buf2[1] = { 0x80 };
 	ASSERT_EQ(readVarint(buf2, buf2 + 1, check), nullptr);
+
+	// Invalid value 3
+	uint8_t buf3[16];
+	memset(buf3, 128, sizeof(buf3));
+	ASSERT_EQ(readVarint(buf3, buf3 + sizeof(buf3), check), nullptr);
+
+	// Invalid value 4
+	uint32_t check2;
+	uint8_t buf4[] = {255, 255, 255, 255, 127};
+	ASSERT_EQ(readVarint(buf4, buf4 + sizeof(buf4), check2), nullptr);
 }
 
 TEST(util, bsr)