diff --git a/src/script/intmath.h b/src/script/intmath.h
new file mode 100644
index 000000000..43d770724
--- /dev/null
+++ b/src/script/intmath.h
@@ -0,0 +1,46 @@
+// Copyright (c) 2021 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#ifndef BITCOIN_SCRIPT_INTMATH_H
+#define BITCOIN_SCRIPT_INTMATH_H
+
+#include <cstdlib>
+#include <limits>
+
+/**
+ * Computes a + b and stores it in result. If the sum overflows or results in an
+ * invalid 63+sign-bit integer, return true, otherwise false. Overflow checks
+ * are emulated and don't rely on built-in overflow checks.
+ */
+static bool AddInt63OverflowEmulated(int64_t a, int64_t b, int64_t &result) {
+    if (a > 0 && b > std::numeric_limits<int64_t>::max() - a) {
+        // integer overflow
+        return true;
+    }
+    if (a < 0 && b <= std::numeric_limits<int64_t>::min() - a) {
+        // integer underflow
+        return true;
+    }
+    result = a + b;
+    return result == std::numeric_limits<int64_t>::min();
+}
+
+/**
+ * Computes a - b and stores it in result. If the difference overflows or
+ * results in an invalid 63+sign-bit integer, return true, otherwise false.
+ * Overflow checks are emulated and don't rely on built-in overflow checks.
+ */
+static bool SubInt63OverflowEmulated(int64_t a, int64_t b, int64_t &result) {
+    if (a < 0 && b > std::numeric_limits<int64_t>::max() + a) {
+        // integer overflow
+        return true;
+    }
+    if (a > 0 && b <= std::numeric_limits<int64_t>::min() + a) {
+        // integer underflow
+        return true;
+    }
+    result = a - b;
+    return result == std::numeric_limits<int64_t>::min();
+}
+
+#endif // BITCOIN_SCRIPT_INTMATH_H
diff --git a/src/test/CMakeLists.txt b/src/test/CMakeLists.txt
index 08aecb183..314a3a6fb 100644
--- a/src/test/CMakeLists.txt
+++ b/src/test/CMakeLists.txt
@@ -1,285 +1,286 @@
 # Copyright (c) 2018 The Bitcoin developers
 
 project(bitcoin-test)
 
 # Process json files.
 file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/data")
 
 function(gen_json_header NAME)
 	set(HEADERS "")
 	foreach(f ${ARGN})
 		set(h "${CMAKE_CURRENT_BINARY_DIR}/${f}.h")
 
 		# Get the proper name for the test variable.
 		get_filename_component(TEST_NAME ${f} NAME_WE)
 		add_custom_command(OUTPUT ${h}
 			COMMAND
 				"${Python_EXECUTABLE}"
 				"${CMAKE_CURRENT_SOURCE_DIR}/data/generate_header.py"
 				"${TEST_NAME}"
 				"${CMAKE_CURRENT_SOURCE_DIR}/${f}" > ${h}
 			MAIN_DEPENDENCY ${f}
 			DEPENDS
 				"data/generate_header.py"
 			VERBATIM
 		)
 		list(APPEND HEADERS ${h})
 	endforeach(f)
 	set(${NAME} "${HEADERS}" PARENT_SCOPE)
 endfunction()
 
 gen_json_header(JSON_HEADERS
 	data/base58_encode_decode.json
 	data/blockfilters.json
 	data/key_io_valid.json
 	data/key_io_invalid.json
 	data/script_tests.json
 	data/sighash.json
 	data/tx_invalid.json
 	data/tx_valid.json
 )
 
 include(TestSuite)
 create_test_suite(bitcoin)
 add_dependencies(check check-bitcoin)
 
 # An utility library for bitcoin related test suites.
 add_library(testutil OBJECT
 	util/blockfilter.cpp
 	util/logging.cpp
 	util/mining.cpp
 	util/net.cpp
 	util/setup_common.cpp
 	util/str.cpp
 	util/transaction_utils.cpp
 	util/wallet.cpp
 )
 
 target_link_libraries(testutil server)
 
 if(BUILD_BITCOIN_WALLET)
 	set(BITCOIN_WALLET_TEST_FIXTURE
 		../wallet/test/init_test_fixture.cpp
 		../wallet/test/wallet_test_fixture.cpp
 	)
 	set(BITCOIN_WALLET_TESTS
 		../wallet/test/db_tests.cpp
 		../wallet/test/coinselector_tests.cpp
 		../wallet/test/init_tests.cpp
 		../wallet/test/ismine_tests.cpp
 		../wallet/test/psbt_wallet_tests.cpp
 		../wallet/test/scriptpubkeyman_tests.cpp
 		../wallet/test/wallet_tests.cpp
 		../wallet/test/walletdb_tests.cpp
 		../wallet/test/wallet_crypto_tests.cpp
 	)
 endif()
 
 function(gen_asmap_headers HEADERS_VAR)
 	foreach(INPUT_FILE ${ARGN})
 		set(OUTPUT_FILE "${CMAKE_CURRENT_BINARY_DIR}/${INPUT_FILE}.h")
 
 		add_custom_command(
 			OUTPUT "${OUTPUT_FILE}"
 			COMMENT "Generate ASMAP header from ${INPUT_FILE}"
 			COMMAND
 				"${Python_EXECUTABLE}"
 				"${CMAKE_CURRENT_SOURCE_DIR}/data/generate_asmap.py"
 				"${CMAKE_CURRENT_SOURCE_DIR}/${INPUT_FILE}"
 				"${OUTPUT_FILE}"
 			MAIN_DEPENDENCY "${INPUT_FILE}"
 			DEPENDS
 				"data/generate_header.py"
 			VERBATIM
 		)
 		list(APPEND ${HEADERS_VAR} "${OUTPUT_FILE}")
 	endforeach()
 	set(${HEADERS_VAR} ${${HEADERS_VAR}} PARENT_SCOPE)
 endfunction()
 
 gen_asmap_headers(ASMAP_HEADERS
 	data/asmap.raw
 )
 
 add_boost_unit_tests_to_suite(bitcoin test_bitcoin
 	fixture.cpp
 	jsonutil.cpp
 	scriptflags.cpp
 	sigutil.cpp
 
 	${ASMAP_HEADERS}
 
 	# Tests generated from JSON
 	${JSON_HEADERS}
 
 	# Wallet test fixture
 	${BITCOIN_WALLET_TEST_FIXTURE}
 
 	TESTS
 		activation_tests.cpp
 		addrman_tests.cpp
 		allocator_tests.cpp
 		amount_tests.cpp
 		arith_uint256_tests.cpp
 		base32_tests.cpp
 		base58_tests.cpp
 		base64_tests.cpp
 		bip32_tests.cpp
 		bitmanip_tests.cpp
 		blockchain_tests.cpp
 		blockcheck_tests.cpp
 		blockencodings_tests.cpp
 		blockfilter_tests.cpp
 		blockfilter_index_tests.cpp
 		blockindex_tests.cpp
 		blockstatus_tests.cpp
 		bloom_tests.cpp
 		bswap_tests.cpp
 		cashaddr_tests.cpp
 		cashaddrenc_tests.cpp
 		checkdatasig_tests.cpp
 		checkpoints_tests.cpp
 		checkqueue_tests.cpp
 		coins_tests.cpp
 		compilerbug_tests.cpp
 		compress_tests.cpp
 		config_tests.cpp
 		core_io_tests.cpp
 		crypto_tests.cpp
 		cuckoocache_tests.cpp
 		dbwrapper_tests.cpp
 		denialofservice_tests.cpp
 		descriptor_tests.cpp
 		dnsseeds_tests.cpp
 		dstencode_tests.cpp
 		feerate_tests.cpp
 		finalization_tests.cpp
 		flatfile_tests.cpp
 		fs_tests.cpp
 		getarg_tests.cpp
 		hash_tests.cpp
 		interfaces_tests.cpp
+		intmath_tests.cpp
 		inv_tests.cpp
 		key_io_tests.cpp
 		key_tests.cpp
 		lcg_tests.cpp
 		logging_tests.cpp
 		mempool_tests.cpp
 		merkle_tests.cpp
 		merkleblock_tests.cpp
 		miner_tests.cpp
 		monolith_opcodes_tests.cpp
 		multisig_tests.cpp
 		net_tests.cpp
 		netbase_tests.cpp
 		op_reversebytes_tests.cpp
 		pmt_tests.cpp
 		policy_fee_tests.cpp
 		policyestimator_tests.cpp
 		prevector_tests.cpp
 		radix_tests.cpp
 		raii_event_tests.cpp
 		random_tests.cpp
 		rcu_tests.cpp
 		ref_tests.cpp
 		reverselock_tests.cpp
 		rpc_tests.cpp
 		rpc_server_tests.cpp
 		rwcollection_tests.cpp
 		sanity_tests.cpp
 		scheduler_tests.cpp
 		schnorr_tests.cpp
 		script_bitfield_tests.cpp
 		script_commitment_tests.cpp
 		script_p2sh_tests.cpp
 		script_standard_tests.cpp
 		script_tests.cpp
 		scriptnum_tests.cpp
 		serialize_tests.cpp
 		settings_tests.cpp
 		sigcache_tests.cpp
 		sigencoding_tests.cpp
 		sighash_tests.cpp
 		sighashtype_tests.cpp
 		sigcheckcount_tests.cpp
 		skiplist_tests.cpp
 		streams_tests.cpp
 		sync_tests.cpp
 		timedata_tests.cpp
 		torcontrol_tests.cpp
 		transaction_tests.cpp
 		txindex_tests.cpp
 		txrequest_tests.cpp
 		txvalidation_tests.cpp
 		txvalidationcache_tests.cpp
 		uint256_tests.cpp
 		undo_tests.cpp
 		util_tests.cpp
 		util_threadnames_tests.cpp
 		validation_block_tests.cpp
 		validation_chainstate_tests.cpp
 		validation_chainstatemanager_tests.cpp
 		validation_flush_tests.cpp
 		validation_tests.cpp
 		validationinterface_tests.cpp
 		versionbits_tests.cpp
 		work_comparator_tests.cpp
 
 		# RPC Tests
 		../rpc/test/server_tests.cpp
 
 		# Wallet tests
 		${BITCOIN_WALLET_TESTS}
 )
 
 function(add_boost_test_runners_with_upgrade_activated SUITE EXECUTABLE)
 	set(SUITE_UPGRADE_ACTIVATED "${SUITE}-upgrade-activated")
 	get_target_from_suite(${SUITE_UPGRADE_ACTIVATED} TARGET_UPGRADE_ACTIVATED)
 
 	if(NOT TARGET ${TARGET_UPGRADE_ACTIVATED})
 		create_test_suite_with_parent_targets(
 			${SUITE_UPGRADE_ACTIVATED}
 			check-upgrade-activated
 			check-upgrade-activated-extended
 		)
 		add_dependencies(${TARGET_UPGRADE_ACTIVATED} ${EXECUTABLE})
 	endif()
 
 	get_target_from_suite(${SUITE} SUITE_TARGET)
 	get_target_property(BOOST_TESTS ${SUITE_TARGET} UNIT_TESTS)
 
 	get_target_from_suite(${SUITE_UPGRADE_ACTIVATED} SUITE_UPGRADE_ACTIVATED_TARGET)
 
 	set(HRF_LOGGER "HRF,test_suite")
 
 	foreach(_test_name ${BOOST_TESTS})
 		if(ENABLE_JUNIT_REPORT)
 			set(JUNIT_LOGGER ":JUNIT,message,${SUITE_UPGRADE_ACTIVATED}-${_test_name}.xml")
 		endif()
 
 		add_test_runner(
 			${SUITE_UPGRADE_ACTIVATED}
 			"${_test_name}"
 			${EXECUTABLE}
 			JUNIT
 			"--run_test=${_test_name}"
 			"--logger=${HRF_LOGGER}${JUNIT_LOGGER}"
 			"--catch_system_errors=no"
 			# Dec. 1st, 2019 at 00:00:00
 			--
 			"-testsuitename=Bitcoin ABC unit tests with next upgrade activated"
 			-axionactivationtime=1575158400
 		)
 	endforeach()
 endfunction()
 
 add_boost_test_runners_with_upgrade_activated(bitcoin test_bitcoin)
 
 target_link_libraries(test_bitcoin rpcclient testutil)
 if(TARGET bitcoinconsensus-shared)
 	target_link_libraries(test_bitcoin bitcoinconsensus-shared)
 else()
 	target_link_libraries(test_bitcoin bitcoinconsensus)
 endif()
 
 add_subdirectory(fuzz)
diff --git a/src/test/intmath_tests.cpp b/src/test/intmath_tests.cpp
new file mode 100644
index 000000000..597c410db
--- /dev/null
+++ b/src/test/intmath_tests.cpp
@@ -0,0 +1,147 @@
+// Copyright (c) 2021 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <boost/test/unit_test.hpp>
+#include <test/lcg.h>
+#include <test/util/setup_common.h>
+
+#include <script/intmath.h>
+
+#include <boost/multiprecision/cpp_int.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(intmath_tests, BasicTestingSetup)
+
+typedef boost::multiprecision::checked_int128_t i128_t;
+
+const i128_t MAX_SCRIPT_63_BIT_INT = 0x7fff'ffff'ffff'ffff;
+const i128_t MIN_SCRIPT_63_BIT_INT = -0x7fff'ffff'ffff'ffff;
+
+const static std::vector<int64_t> INTERESTING_63_BIT_NUMBERS({
+    0,
+    1,
+    -1,
+    2,
+    -2,
+    4,
+    -4,
+    10,
+    -10,
+    100,
+    -100,
+    127,
+    -127,
+    255,
+    -255,
+    256,
+    -256,
+    1000,
+    -1000,
+    5040,
+    -5040,
+    0x7fff,
+    -0x7fff,
+    0x1'0000,
+    -0x1'0000,
+    0x7f'ffff,
+    -0x7f'ffff,
+    0x100'0000,
+    -0x100'0000,
+    0x7fff'ffff,
+    -0x7fff'ffff,
+    0xffff'ffff,
+    -0xffff'ffff,
+    0x1'0000'0000,
+    -0x1'0000'0000,
+    0x7f'ffff'ffff,
+    -0x7f'ffff'ffff,
+    0xff'ffff'ffff,
+    -0xff'ffff'ffff,
+    0x100'0000'0000,
+    -0x100'0000'0000,
+    0x7fff'ffff'ffff,
+    -0x7fff'ffff'ffff,
+    0xffff'ffff'ffff,
+    -0xffff'ffff'ffff,
+    0x1'0000'0000'0000,
+    -0x1'0000'0000'0000,
+    0x7f'ffff'ffff'ffff,
+    -0x7f'ffff'ffff'ffff,
+    0xff'ffff'ffff'ffff,
+    -0xff'ffff'ffff'ffff,
+    0x100'0000'0000'0000,
+    -0x100'0000'0000'0000,
+    0x7fff'ffff'ffff'ffff,
+    -0x7fff'ffff'ffff'ffff,
+});
+
+bool IsInScriptBounds(const i128_t &num_int) {
+    return num_int >= MIN_SCRIPT_63_BIT_INT && num_int <= MAX_SCRIPT_63_BIT_INT;
+}
+
+void CheckArithmetic(const int64_t a_64, const int64_t b_64) {
+    const i128_t a = a_64;
+    const i128_t b = b_64;
+    {
+        // Test AddInt63OverflowEmulated
+        int64_t result;
+        bool expect_overflow = !IsInScriptBounds(a + b);
+        bool had_overflow = AddInt63OverflowEmulated(a_64, b_64, result);
+        if (expect_overflow) {
+            BOOST_CHECK_MESSAGE(
+                had_overflow, strprintf("%d + %d didn't overflow", a_64, b_64));
+        } else {
+            BOOST_CHECK_MESSAGE(!had_overflow,
+                                strprintf("%d + %d overflowed", a_64, b_64));
+            BOOST_CHECK_EQUAL(result, a + b);
+        }
+    }
+    {
+        // Test SubInt63OverflowEmulated
+        int64_t result;
+        bool expect_overflow = !IsInScriptBounds(a - b);
+        bool had_overflow = SubInt63OverflowEmulated(a_64, b_64, result);
+        if (expect_overflow) {
+            BOOST_CHECK_MESSAGE(
+                had_overflow, strprintf("%d - %d didn't overflow", a_64, b_64));
+        } else {
+            BOOST_CHECK_MESSAGE(!had_overflow,
+                                strprintf("%d - %d overflowed", a_64, b_64));
+            BOOST_CHECK_EQUAL(result, a - b);
+        }
+    }
+}
+
+/** Generate random number in [-2^63; 2^63]. */
+int64_t GenInt63(MMIXLinearCongruentialGenerator &lcg) {
+    while (true) {
+        // Uniform number in [-2^63; 2^63].
+        int64_t val = (int64_t(lcg.next()) << 32) | lcg.next();
+        // Make bit-length uniformly distributed for better test coverage.
+        val >>= (lcg.next() % 64);
+        // Ensure value is in bounds.
+        if (val != std::numeric_limits<int64_t>::min()) {
+            return val;
+        }
+    }
+}
+
+BOOST_AUTO_TEST_CASE(check_arithmetic) {
+    MMIXLinearCongruentialGenerator lcg;
+    for (uint32_t test = 0; test < 2048; ++test) {
+        int64_t a = GenInt63(lcg);
+        int64_t b = GenInt63(lcg);
+        CheckArithmetic(a, b);
+        for (const int64_t &num : INTERESTING_63_BIT_NUMBERS) {
+            CheckArithmetic(a, num);
+            CheckArithmetic(num, b);
+        }
+    }
+    for (const int64_t &a : INTERESTING_63_BIT_NUMBERS) {
+        for (const int64_t &b : INTERESTING_63_BIT_NUMBERS) {
+            CheckArithmetic(a, b);
+        }
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/test/lint/lint-boost-dependencies.sh b/test/lint/lint-boost-dependencies.sh
index a404b86db..0601b02be 100755
--- a/test/lint/lint-boost-dependencies.sh
+++ b/test/lint/lint-boost-dependencies.sh
@@ -1,64 +1,65 @@
 #!/usr/bin/env bash
 #
 # Copyright (c) 2018 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 #
 # Guard against accidental introduction of new Boost dependencies.
 
 export LC_ALL=C
 
 EXPECTED_BOOST_INCLUDES=(
     boost/algorithm/string.hpp
     boost/algorithm/string/classification.hpp
     boost/algorithm/string/replace.hpp
     boost/algorithm/string/split.hpp
     boost/date_time/posix_time/posix_time.hpp
     boost/filesystem.hpp
     boost/filesystem/fstream.hpp
+    boost/multiprecision/cpp_int.hpp
     boost/multi_index/composite_key.hpp
     boost/multi_index/hashed_index.hpp
     boost/multi_index/member.hpp
     boost/multi_index/ordered_index.hpp
     boost/multi_index/sequenced_index.hpp
     boost/multi_index_container.hpp
     boost/preprocessor/cat.hpp
     boost/preprocessor/stringize.hpp
     boost/range/iterator.hpp
     boost/range/adaptor/sliced.hpp
     boost/signals2/connection.hpp
     boost/signals2/last_value.hpp
     boost/signals2/signal.hpp
     boost/test/unit_test.hpp
     boost/thread/condition_variable.hpp
     boost/thread/mutex.hpp
     boost/thread/shared_mutex.hpp
     boost/thread/thread.hpp
     boost/variant.hpp
     boost/variant/apply_visitor.hpp
     boost/variant/static_visitor.hpp
 )
 
 for BOOST_INCLUDE in $(git grep '^#include <boost/' -- "*.cpp" "*.h" | cut -f2 -d: | cut -f2 -d'<' | cut -f1 -d'>' | sort -u); do
     IS_EXPECTED_INCLUDE=0
     for EXPECTED_BOOST_INCLUDE in "${EXPECTED_BOOST_INCLUDES[@]}"; do
         if [[ "${BOOST_INCLUDE}" == "${EXPECTED_BOOST_INCLUDE}" ]]; then
             IS_EXPECTED_INCLUDE=1
             break
         fi
     done
     if [[ ${IS_EXPECTED_INCLUDE} == 0 ]]; then
         echo "A new Boost dependency in the form of \"${BOOST_INCLUDE}\" appears to have been introduced:"
         git grep "${BOOST_INCLUDE}" -- "*.cpp" "*.h"
         echo
     fi
 done
 
 for EXPECTED_BOOST_INCLUDE in "${EXPECTED_BOOST_INCLUDES[@]}"; do
     if ! git grep -q "^#include <${EXPECTED_BOOST_INCLUDE}>" -- "*.cpp" "*.h"; then
         echo "Good job! The Boost dependency \"${EXPECTED_BOOST_INCLUDE}\" is no longer used."
         echo "Please remove it from EXPECTED_BOOST_INCLUDES in $0"
         echo "to make sure this dependency is not accidentally reintroduced."
         echo
     fi
 done