diff --git a/test/statetest/statetest.hpp b/test/statetest/statetest.hpp
index 29a4ecf1c9..f6808b4cff 100644
--- a/test/statetest/statetest.hpp
+++ b/test/statetest/statetest.hpp
@@ -68,6 +68,12 @@ struct StateTransitionTest
 template <typename T>
 T from_json(const json::json& j) = delete;
 
+template <>
+uint64_t from_json<uint64_t>(const json::json& j);
+
+template <>
+int64_t from_json<int64_t>(const json::json& j);
+
 template <>
 state::BlockInfo from_json<state::BlockInfo>(const json::json& j);
 
diff --git a/test/statetest/statetest_loader.cpp b/test/statetest/statetest_loader.cpp
index 83997c316d..6c21f89364 100644
--- a/test/statetest/statetest_loader.cpp
+++ b/test/statetest/statetest_loader.cpp
@@ -23,13 +23,23 @@ uint8_t from_json<uint8_t>(const json::json& j)
 template <>
 int64_t from_json<int64_t>(const json::json& j)
 {
-    return static_cast<int64_t>(std::stoll(j.get<std::string>(), nullptr, 16));
+    if (j.is_number_integer())
+        return j.get<int64_t>();
+    else if (j.is_string())
+        return std::stoll(j.get<std::string>(), nullptr, 0);
+    else
+        throw std::invalid_argument("from_json<int64_t>: must be string or number");
 }
 
 template <>
 uint64_t from_json<uint64_t>(const json::json& j)
 {
-    return static_cast<uint64_t>(std::stoull(j.get<std::string>(), nullptr, 16));
+    if (j.is_number_integer())
+        return j.get<uint64_t>();
+    else if (j.is_string())
+        return std::stoull(j.get<std::string>(), nullptr, 0);
+    else
+        throw std::invalid_argument("from_json<uint64_t>: must be string or number");
 }
 
 template <>
diff --git a/test/unittests/CMakeLists.txt b/test/unittests/CMakeLists.txt
index 24461911d1..37ef6ca117 100644
--- a/test/unittests/CMakeLists.txt
+++ b/test/unittests/CMakeLists.txt
@@ -31,6 +31,7 @@ target_sources(
     evmone_test.cpp
     execution_state_test.cpp
     instructions_test.cpp
+    json_loader_test.cpp
     state_bloom_filter_test.cpp
     state_mpt_hash_test.cpp
     state_mpt_test.cpp
diff --git a/test/unittests/json_loader_test.cpp b/test/unittests/json_loader_test.cpp
new file mode 100644
index 0000000000..b853998bc7
--- /dev/null
+++ b/test/unittests/json_loader_test.cpp
@@ -0,0 +1,57 @@
+// evmone: Fast Ethereum Virtual Machine implementation
+// Copyright 2023 The evmone Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+#include <gtest/gtest.h>
+#include <test/statetest/statetest.hpp>
+
+using namespace evmone;
+
+TEST(json_loader, uint64_t)
+{
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json("0x00000005")), 5);
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json("5")), 5);
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json(7)), 7);
+
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json("0xffffffffffffffff")),
+        std::numeric_limits<uint64_t>::max());
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json("18446744073709551615")),
+        std::numeric_limits<uint64_t>::max());
+    EXPECT_THROW(
+        test::from_json<uint64_t>(json::basic_json("0x10000000000000000")), std::out_of_range);
+    EXPECT_THROW(
+        test::from_json<uint64_t>(json::basic_json("18446744073709551616")), std::out_of_range);
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json(0xffffffffffffffff)),
+        std::numeric_limits<uint64_t>::max());
+
+    // TODO: Isn't it a little strange behaviour of std::stoull?
+    EXPECT_EQ(test::from_json<uint64_t>(json::basic_json("0x000000000000000k")), 0);
+    EXPECT_THROW(test::from_json<uint64_t>(json::basic_json("k")), std::invalid_argument);
+}
+
+TEST(json_loader, int64_t)
+{
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("0x00000005")), 5);
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("-0x5")), -5);
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("-5")), -5);
+
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json(-7)), -7);
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json(0xffffffffffffffff)), -1);
+
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("0x7fffffffffffffff")),
+        std::numeric_limits<int64_t>::max());
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("9223372036854775807")),
+        std::numeric_limits<int64_t>::max());
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("-9223372036854775808")),
+        std::numeric_limits<int64_t>::min());
+    EXPECT_THROW(
+        test::from_json<int64_t>(json::basic_json("0xffffffffffffffff")), std::out_of_range);
+    EXPECT_THROW(
+        test::from_json<int64_t>(json::basic_json("9223372036854775808")), std::out_of_range);
+    EXPECT_THROW(
+        test::from_json<int64_t>(json::basic_json("-9223372036854775809")), std::out_of_range);
+
+    // TODO: Isn't it a little strange behaviour of std::stoull?
+    EXPECT_EQ(test::from_json<int64_t>(json::basic_json("0x000000000000000k")), 0);
+    EXPECT_THROW(test::from_json<int64_t>(json::basic_json("k")), std::invalid_argument);
+}
diff --git a/test/unittests/statetest_loader_block_info_test.cpp b/test/unittests/statetest_loader_block_info_test.cpp
index 9c44642598..09c2cb4b11 100644
--- a/test/unittests/statetest_loader_block_info_test.cpp
+++ b/test/unittests/statetest_loader_block_info_test.cpp
@@ -23,7 +23,7 @@ TEST(statetest_loader, block_info)
     const auto bi = test::from_json<state::BlockInfo>(json::json::parse(input));
     EXPECT_EQ(bi.coinbase, 0x1111111111111111111111111111111111111111_address);
     EXPECT_EQ(
-        bi.prev_randao, 0x0000000000000000000000000000000000000000000000000000000000000000_bytes32);
+        bi.prev_randao, 0x00_bytes32);
     EXPECT_EQ(bi.gas_limit, 0x0);
     EXPECT_EQ(bi.base_fee, 7);
     EXPECT_EQ(bi.timestamp, 0);
@@ -55,7 +55,7 @@ TEST(statetest_loader, block_info_hex)
     const auto bi = test::from_json<state::BlockInfo>(json::json::parse(input));
     EXPECT_EQ(bi.coinbase, 0x2adc25665018aa1fe0e6bc666dac8fc2697ff9ba_address);
     EXPECT_EQ(
-        bi.prev_randao, 0x0000000000000000000000000000000000000000000000000000000000000000_bytes32);
+        bi.prev_randao, 0x00_bytes32);
     EXPECT_EQ(bi.gas_limit, 100000000000000000);
     EXPECT_EQ(bi.base_fee, 7);
     EXPECT_EQ(bi.timestamp, 1000);
@@ -87,7 +87,7 @@ TEST(statetest_loader, block_info_dec)
     const auto bi = test::from_json<state::BlockInfo>(json::json::parse(input));
     EXPECT_EQ(bi.coinbase, 0x2adc25665018aa1fe0e6bc666dac8fc2697ff9ba_address);
     EXPECT_EQ(
-        bi.prev_randao, 0x0000000000000000000000000000000000000000000000000000000000000000_bytes32);
+        bi.prev_randao, 0x00_bytes32);
     EXPECT_EQ(bi.gas_limit, 100000000000000000);
     EXPECT_EQ(bi.base_fee, 7);
     EXPECT_EQ(bi.timestamp, 1000);
@@ -110,7 +110,7 @@ TEST(statetest_loader, block_info_0_random)
     const auto bi = test::from_json<state::BlockInfo>(json::json::parse(input));
     EXPECT_EQ(bi.coinbase, 0x1111111111111111111111111111111111111111_address);
     EXPECT_EQ(
-        bi.prev_randao, 0x0000000000000000000000000000000000000000000000000000000000000000_bytes32);
+        bi.prev_randao, 0x00_bytes32);
     EXPECT_EQ(bi.gas_limit, 0x0);
     EXPECT_EQ(bi.base_fee, 7);
     EXPECT_EQ(bi.timestamp, 0);
diff --git a/test/unittests/statetest_loader_tx_test.cpp b/test/unittests/statetest_loader_tx_test.cpp
index fdad282f6f..07a1c50526 100644
--- a/test/unittests/statetest_loader_tx_test.cpp
+++ b/test/unittests/statetest_loader_tx_test.cpp
@@ -15,7 +15,7 @@ TEST(statetest_loader, tx_create_legacy)
 {
     constexpr std::string_view input = R"({
         "input": "b0b1",
-        "gas": "9091",
+        "gas": "0x9091",
         "value": "0xe0e1",
         "sender": "a0a1",
         "to": "",
@@ -46,7 +46,7 @@ TEST(statetest_loader, tx_eip1559)
 {
     constexpr std::string_view input = R"({
         "input": "b0b1",
-        "gas": "9091",
+        "gas": "0x9091",
         "value": "0xe0e1",
         "sender": "a0a1",
         "to": "c0c1",