diff --git a/src/test/fuzz/CMakeLists.txt b/src/test/fuzz/CMakeLists.txt
--- a/src/test/fuzz/CMakeLists.txt
+++ b/src/test/fuzz/CMakeLists.txt
@@ -79,17 +79,20 @@
 	asmap
 	base_encode_decode
 	block
+	block_header
 	bloom_filter
 	rolling_bloom_filter
 	cashaddr
 	descriptor_parse
 	eval_script
+	fee_rate
 	float
 	hex
 	integer
 	key
 	key_io
 	locale
+	multiplication_overflow
 	net_permissions
 	netaddress
 	p2p_transport_deserializer
@@ -106,6 +109,7 @@
 	script_ops
 	scriptnum_ops
 	spanparsing
+	string
 	strprintf
 	timedata
 	transaction
diff --git a/src/test/fuzz/block_header.cpp b/src/test/fuzz/block_header.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/fuzz/block_header.cpp
@@ -0,0 +1,43 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <primitives/block.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+#include <uint256.h>
+
+#include <cassert>
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t> &buffer) {
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const std::optional<CBlockHeader> block_header =
+        ConsumeDeserializable<CBlockHeader>(fuzzed_data_provider);
+    if (!block_header) {
+        return;
+    }
+    {
+        const BlockHash hash = block_header->GetHash();
+        static const BlockHash blockhash_max(
+            uint256S("fffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
+                     "fffffff"));
+        assert(hash != blockhash_max);
+        assert(block_header->GetBlockTime() == block_header->nTime);
+        assert(block_header->IsNull() == (block_header->nBits == 0));
+    }
+    {
+        CBlockHeader mut_block_header = *block_header;
+        mut_block_header.SetNull();
+        assert(mut_block_header.IsNull());
+        CBlock block{*block_header};
+        assert(block.GetBlockHeader().GetHash() == block_header->GetHash());
+        (void)block.ToString();
+        block.SetNull();
+        assert(block.GetBlockHeader().GetHash() == mut_block_header.GetHash());
+    }
+}
diff --git a/src/test/fuzz/fee_rate.cpp b/src/test/fuzz/fee_rate.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/fuzz/fee_rate.cpp
@@ -0,0 +1,40 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <amount.h>
+#include <feerate.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cstdint>
+#include <limits>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t> &buffer) {
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const Amount satoshis_per_k = ConsumeMoney(fuzzed_data_provider);
+    const CFeeRate fee_rate{satoshis_per_k};
+
+    (void)fee_rate.GetFeePerK();
+    const size_t bytes = fuzzed_data_provider.ConsumeIntegral<size_t>();
+    if (bytes <= uint64_t(std::numeric_limits<int64_t>::max())) {
+        (void)fee_rate.GetFee(bytes);
+    }
+    (void)fee_rate.ToString();
+
+    const Amount another_satoshis_per_k = ConsumeMoney(fuzzed_data_provider);
+    CFeeRate larger_fee_rate{another_satoshis_per_k};
+    larger_fee_rate += fee_rate;
+    if (satoshis_per_k != Amount::zero() &&
+        another_satoshis_per_k != Amount::zero()) {
+        assert(fee_rate < larger_fee_rate);
+        assert(!(fee_rate > larger_fee_rate));
+        assert(!(fee_rate == larger_fee_rate));
+        assert(fee_rate <= larger_fee_rate);
+        assert(!(fee_rate >= larger_fee_rate));
+        assert(fee_rate != larger_fee_rate);
+    }
+}
diff --git a/src/test/fuzz/integer.cpp b/src/test/fuzz/integer.cpp
--- a/src/test/fuzz/integer.cpp
+++ b/src/test/fuzz/integer.cpp
@@ -11,6 +11,7 @@
 #include <core_io.h>
 #include <crypto/common.h>
 #include <crypto/siphash.h>
+#include <ctime>
 #include <key_io.h>
 #include <memusage.h>
 #include <netbase.h>
@@ -35,6 +36,7 @@
 #include <test/fuzz/fuzz.h>
 
 #include <cassert>
+#include <chrono>
 #include <limits>
 #include <vector>
 
@@ -139,6 +141,8 @@
             assert(parsed_money == i64 * SATOSHI);
         }
     }
+    const std::chrono::seconds seconds{i64};
+    assert(count_seconds(seconds) == i64);
 
     const arith_uint256 au256 = UintToArith256(u256);
     assert(ArithToUint256(au256) == u256);
diff --git a/src/test/fuzz/multiplication_overflow.cpp b/src/test/fuzz/multiplication_overflow.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/fuzz/multiplication_overflow.cpp
@@ -0,0 +1,42 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace {
+template <typename T>
+void TestMultiplicationOverflow(FuzzedDataProvider &fuzzed_data_provider) {
+    const T i = fuzzed_data_provider.ConsumeIntegral<T>();
+    const T j = fuzzed_data_provider.ConsumeIntegral<T>();
+    const bool is_multiplication_overflow_custom = MultiplicationOverflow(i, j);
+    T result_builtin;
+    const bool is_multiplication_overflow_builtin =
+        __builtin_mul_overflow(i, j, &result_builtin);
+    assert(is_multiplication_overflow_custom ==
+           is_multiplication_overflow_builtin);
+    if (!is_multiplication_overflow_custom) {
+        assert(i * j == result_builtin);
+    }
+}
+} // namespace
+
+void test_one_input(const std::vector<uint8_t> &buffer) {
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    TestMultiplicationOverflow<int64_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<uint64_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<int32_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<uint32_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<int16_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<uint16_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<char>(fuzzed_data_provider);
+    TestMultiplicationOverflow<uint8_t>(fuzzed_data_provider);
+    TestMultiplicationOverflow<signed char>(fuzzed_data_provider);
+    TestMultiplicationOverflow<bool>(fuzzed_data_provider);
+}
diff --git a/src/test/fuzz/string.cpp b/src/test/fuzz/string.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/fuzz/string.cpp
@@ -0,0 +1,98 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <blockfilter.h>
+#include <clientversion.h>
+#include <logging.h>
+#include <netbase.h>
+#include <outputtype.h>
+#include <rpc/client.h>
+#include <rpc/request.h>
+#include <rpc/server.h>
+#include <rpc/util.h>
+#include <script/descriptor.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+#include <util/error.h>
+#include <util/message.h>
+#include <util/settings.h>
+#include <util/strencodings.h>
+#include <util/string.h>
+#include <util/system.h>
+#include <util/translation.h>
+#include <util/url.h>
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t> &buffer) {
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const std::string random_string_1 =
+        fuzzed_data_provider.ConsumeRandomLengthString(32);
+    const std::string random_string_2 =
+        fuzzed_data_provider.ConsumeRandomLengthString(32);
+    const std::vector<std::string> random_string_vector =
+        ConsumeRandomLengthStringVector(fuzzed_data_provider);
+
+    (void)AmountErrMsg(random_string_1, random_string_2);
+    (void)AmountHighWarn(random_string_1);
+    BlockFilterType block_filter_type;
+    (void)BlockFilterTypeByName(random_string_1, block_filter_type);
+    (void)Capitalize(random_string_1);
+    (void)CopyrightHolders(random_string_1);
+    (void)FormatParagraph(
+        random_string_1,
+        fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, 1000),
+        fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, 1000));
+    (void)FormatSubVersion(random_string_1,
+                           fuzzed_data_provider.ConsumeIntegral<int>(),
+                           random_string_vector);
+    (void)GetDescriptorChecksum(random_string_1);
+    (void)HelpExampleCli(random_string_1, random_string_2);
+    (void)HelpExampleRpc(random_string_1, random_string_2);
+    (void)HelpMessageGroup(random_string_1);
+    (void)HelpMessageOpt(random_string_1, random_string_2);
+    ArgsManager argsman;
+    (void)IsDeprecatedRPCEnabled(argsman, random_string_1);
+    (void)Join(random_string_vector, random_string_1);
+    (void)JSONRPCError(fuzzed_data_provider.ConsumeIntegral<int>(),
+                       random_string_1);
+    const util::Settings settings;
+    (void)OnlyHasDefaultSectionSetting(settings, random_string_1,
+                                       random_string_2);
+    (void)ParseNetwork(random_string_1);
+    try {
+        (void)ParseNonRFCJSONValue(random_string_1);
+    } catch (const std::runtime_error &) {
+    }
+    OutputType output_type;
+    (void)ParseOutputType(random_string_1, output_type);
+    (void)ResolveErrMsg(random_string_1, random_string_2);
+    try {
+        (void)RPCConvertNamedValues(random_string_1, random_string_vector);
+    } catch (const std::runtime_error &) {
+    }
+    try {
+        (void)RPCConvertValues(random_string_1, random_string_vector);
+    } catch (const std::runtime_error &) {
+    }
+    (void)SanitizeString(random_string_1);
+    (void)SanitizeString(
+        random_string_1,
+        fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 3));
+    (void)ShellEscape(random_string_1);
+    int port_out;
+    std::string host_out;
+    SplitHostPort(random_string_1, port_out, host_out);
+    (void)TimingResistantEqual(random_string_1, random_string_2);
+    (void)ToLower(random_string_1);
+    (void)ToUpper(random_string_1);
+    (void)TrimString(random_string_1);
+    (void)TrimString(random_string_1, random_string_2);
+    (void)urlDecode(random_string_1);
+    (void)ValidAsCString(random_string_1);
+    (void)_(random_string_1.c_str());
+}
diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -5,6 +5,7 @@
 #ifndef BITCOIN_TEST_FUZZ_UTIL_H
 #define BITCOIN_TEST_FUZZ_UTIL_H
 
+#include <amount.h>
 #include <attributes.h>
 #include <script/script.h>
 #include <serialize.h>
@@ -25,6 +26,20 @@
     return {s.begin(), s.end()};
 }
 
+NODISCARD inline std::vector<std::string>
+ConsumeRandomLengthStringVector(FuzzedDataProvider &fuzzed_data_provider,
+                                size_t max_vector_size = 16,
+                                size_t max_string_length = 16) noexcept {
+    const size_t n_elements =
+        fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
+    std::vector<std::string> r;
+    for (size_t i = 0; i < n_elements; ++i) {
+        r.push_back(
+            fuzzed_data_provider.ConsumeRandomLengthString(max_string_length));
+    }
+    return r;
+}
+
 template <typename T>
 NODISCARD inline std::optional<T>
 ConsumeDeserializable(FuzzedDataProvider &fuzzed_data_provider,
@@ -47,6 +62,15 @@
         fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(0, MAX_OPCODE));
 }
 
+NODISCARD inline Amount
+ConsumeMoney(FuzzedDataProvider &fuzzed_data_provider) noexcept {
+    // FIXME find a better way to avoid duplicating the MAX_MONEY definition
+    int64_t maxMoneyAsInt = int64_t(21000000) * int64_t(100000000);
+    return fuzzed_data_provider.ConsumeIntegralInRange<int64_t>(0,
+                                                                maxMoneyAsInt) *
+           SATOSHI;
+}
+
 NODISCARD inline CScript
 ConsumeScript(FuzzedDataProvider &fuzzed_data_provider) noexcept {
     const std::vector<uint8_t> b =
@@ -59,4 +83,25 @@
     return CScriptNum{fuzzed_data_provider.ConsumeIntegral<int64_t>()};
 }
 
+template <typename T> bool MultiplicationOverflow(T i, T j) {
+    static_assert(std::is_integral<T>::value, "Integral required.");
+    if (std::numeric_limits<T>::is_signed) {
+        if (i > 0) {
+            if (j > 0) {
+                return i > (std::numeric_limits<T>::max() / j);
+            } else {
+                return j < (std::numeric_limits<T>::min() / i);
+            }
+        } else {
+            if (j > 0) {
+                return i < (std::numeric_limits<T>::min() / j);
+            } else {
+                return i != 0 && (j < (std::numeric_limits<T>::max() / i));
+            }
+        }
+    } else {
+        return j != 0 && i > std::numeric_limits<T>::max() / j;
+    }
+}
+
 #endif // BITCOIN_TEST_FUZZ_UTIL_H