diff --git a/src/api/exceptions.cc b/src/api/exceptions.cc
index 4d1cca8b651..897a4de3652 100644
--- a/src/api/exceptions.cc
+++ b/src/api/exceptions.cc
@@ -7,7 +7,7 @@
 #include "uv.h"
 #include "v8.h"
 
-#include <string.h>
+#include <cstring>
 
 namespace node {
 
diff --git a/src/api/utils.cc b/src/api/utils.cc
index e6993f33b00..b0998b6fb76 100644
--- a/src/api/utils.cc
+++ b/src/api/utils.cc
@@ -1,7 +1,7 @@
 #include "node.h"
 #include "node_internals.h"
 
-#include <signal.h>
+#include <csignal>
 
 namespace node {
 
diff --git a/src/async_wrap.h b/src/async_wrap.h
index 6d5da4e4ee1..09319c11bba 100644
--- a/src/async_wrap.h
+++ b/src/async_wrap.h
@@ -27,7 +27,7 @@
 #include "base_object.h"
 #include "v8.h"
 
-#include <stdint.h>
+#include <cstdint>
 
 namespace node {
 
diff --git a/src/base64.h b/src/base64.h
index aedec375eba..ba609704319 100644
--- a/src/base64.h
+++ b/src/base64.h
@@ -5,8 +5,8 @@
 
 #include "util.h"
 
-#include <stddef.h>
-#include <stdint.h>
+#include <cstddef>
+#include <cstdint>
 
 namespace node {
 //// Base 64 ////
diff --git a/src/cares_wrap.cc b/src/cares_wrap.cc
index 91226ebdf7c..dadba4be7b2 100644
--- a/src/cares_wrap.cc
+++ b/src/cares_wrap.cc
@@ -28,8 +28,8 @@
 #include "util-inl.h"
 #include "uv.h"
 
-#include <errno.h>
-#include <string.h>
+#include <cerrno>
+#include <cstring>
 #include <vector>
 #include <unordered_set>
 
diff --git a/src/debug_utils.cc b/src/debug_utils.cc
index fadcaa50619..f1024183cda 100644
--- a/src/debug_utils.cc
+++ b/src/debug_utils.cc
@@ -19,7 +19,7 @@
 #include <execinfo.h>
 #include <unistd.h>
 #include <sys/mman.h>
-#include <stdio.h>
+#include <cstdio>
 #endif
 
 #else  // __POSIX__
diff --git a/src/env-inl.h b/src/env-inl.h
index 63b71daf15a..9752613b292 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -34,8 +34,8 @@
 #include "node_context_data.h"
 #include "node_worker.h"
 
-#include <stddef.h>
-#include <stdint.h>
+#include <cstddef>
+#include <cstdint>
 
 #include <utility>
 
diff --git a/src/env.cc b/src/env.cc
index fce949f63a8..3f30fda3749 100644
--- a/src/env.cc
+++ b/src/env.cc
@@ -14,7 +14,7 @@
 #include "tracing/traced_value.h"
 #include "v8-profiler.h"
 
-#include <stdio.h>
+#include <cstdio>
 #include <algorithm>
 #include <atomic>
 
diff --git a/src/env.h b/src/env.h
index 3856f5241d6..bd8ff761290 100644
--- a/src/env.h
+++ b/src/env.h
@@ -38,7 +38,7 @@
 #include "uv.h"
 #include "v8.h"
 
-#include <stdint.h>
+#include <cstdint>
 #include <functional>
 #include <list>
 #include <unordered_map>
diff --git a/src/inspector_agent.cc b/src/inspector_agent.cc
index 15edf7f00c3..82d96e7ef7f 100644
--- a/src/inspector_agent.cc
+++ b/src/inspector_agent.cc
@@ -16,13 +16,13 @@
 
 #include "libplatform/libplatform.h"
 
-#include <string.h>
+#include <cstring>
 #include <sstream>
 #include <unordered_map>
 #include <vector>
 
 #ifdef __POSIX__
-#include <limits.h>  // PTHREAD_STACK_MIN
+#include <climits>  // PTHREAD_STACK_MIN
 #include <pthread.h>
 #endif  // __POSIX__
 
diff --git a/src/inspector_agent.h b/src/inspector_agent.h
index 905b1e2841e..b8b03b2edc3 100644
--- a/src/inspector_agent.h
+++ b/src/inspector_agent.h
@@ -5,7 +5,7 @@
 
 #include <memory>
 
-#include <stddef.h>
+#include <cstddef>
 
 #if !HAVE_INSPECTOR
 #error("This header can only be used when inspector is enabled")
diff --git a/src/inspector_io.cc b/src/inspector_io.cc
index 42643fa6f6d..161ba276dd9 100644
--- a/src/inspector_io.cc
+++ b/src/inspector_io.cc
@@ -13,7 +13,7 @@
 #include "zlib.h"
 
 #include <deque>
-#include <string.h>
+#include <cstring>
 #include <vector>
 
 namespace node {
diff --git a/src/inspector_io.h b/src/inspector_io.h
index bc09afdd3df..e4b4ee44f81 100644
--- a/src/inspector_io.h
+++ b/src/inspector_io.h
@@ -8,7 +8,7 @@
 #include "uv.h"
 
 #include <memory>
-#include <stddef.h>
+#include <cstddef>
 
 #if !HAVE_INSPECTOR
 #error("This header can only be used when inspector is enabled")
diff --git a/src/inspector_socket.cc b/src/inspector_socket.cc
index 7be9a01e0c4..fd10231af7c 100644
--- a/src/inspector_socket.cc
+++ b/src/inspector_socket.cc
@@ -11,7 +11,7 @@
 #include "openssl/sha.h"  // Sha-1 hash
 
 #include <map>
-#include <string.h>
+#include <cstring>
 
 #define ACCEPT_KEY_LENGTH base64_encoded_size(20)
 #define BUFFER_GROWTH_CHUNK_SIZE 1024
diff --git a/src/module_wrap.cc b/src/module_wrap.cc
index 93e791b5224..3d55d12cc38 100644
--- a/src/module_wrap.cc
+++ b/src/module_wrap.cc
@@ -1,5 +1,5 @@
 #include <algorithm>
-#include <limits.h>  // PATH_MAX
+#include <climits>  // PATH_MAX
 #include <sys/stat.h>  // S_IFDIR
 #include "module_wrap.h"
 
diff --git a/src/node.cc b/src/node.cc
index b3195b73658..e46232405f4 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -72,13 +72,13 @@
 #include "large_pages/node_large_page.h"
 #endif
 
-#include <errno.h>
+#include <cerrno>
 #include <fcntl.h>  // _O_RDWR
-#include <limits.h>  // PATH_MAX
-#include <signal.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <climits>  // PATH_MAX
+#include <csignal>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <sys/types.h>
 
 #include <string>
diff --git a/src/node.h b/src/node.h
index 53fb5fb51a9..3ba5cf92f34 100644
--- a/src/node.h
+++ b/src/node.h
@@ -178,8 +178,8 @@ NODE_DEPRECATED("Use MakeCallback(..., async_context)",
 
 }  // namespace node
 
-#include <assert.h>
-#include <stdint.h>
+#include <cassert>
+#include <cstdint>
 
 #ifndef NODE_STRINGIFY
 #define NODE_STRINGIFY(n) NODE_STRINGIFY_HELPER(n)
diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index aca1842c30b..10b8f4098f2 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -31,8 +31,8 @@
 #include "v8-profiler.h"
 #include "v8.h"
 
-#include <string.h>
-#include <limits.h>
+#include <cstring>
+#include <climits>
 
 #define THROW_AND_RETURN_UNLESS_BUFFER(env, obj)                            \
   THROW_AND_RETURN_IF_NOT_BUFFER(env, obj, "argument")                      \
diff --git a/src/node_constants.cc b/src/node_constants.cc
index debcf0e1004..e4eae1727cb 100644
--- a/src/node_constants.cc
+++ b/src/node_constants.cc
@@ -24,12 +24,12 @@
 
 #include "zlib.h"
 
-#include <errno.h>
+#include <cerrno>
 #if !defined(_MSC_VER)
 #include <unistd.h>
 #endif
 #include <fcntl.h>
-#include <signal.h>
+#include <csignal>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <limits>
diff --git a/src/node_crypto.cc b/src/node_crypto.cc
index 49b9dfe576c..dcdecb50648 100644
--- a/src/node_crypto.cc
+++ b/src/node_crypto.cc
@@ -37,9 +37,9 @@
 #include "util-inl.h"
 #include "v8.h"
 
-#include <errno.h>
-#include <limits.h>  // INT_MAX
-#include <string.h>
+#include <cerrno>
+#include <climits>  // INT_MAX
+#include <cstring>
 
 #include <algorithm>
 #include <memory>
diff --git a/src/node_crypto_bio.cc b/src/node_crypto_bio.cc
index baa90204f2f..31165b7c988 100644
--- a/src/node_crypto_bio.cc
+++ b/src/node_crypto_bio.cc
@@ -22,8 +22,8 @@
 #include "node_crypto_bio.h"
 #include "openssl/bio.h"
 #include "util-inl.h"
-#include <limits.h>
-#include <string.h>
+#include <climits>
+#include <cstring>
 
 namespace node {
 namespace crypto {
diff --git a/src/node_crypto_clienthello.h b/src/node_crypto_clienthello.h
index 48f49771fdf..d1661735f5d 100644
--- a/src/node_crypto_clienthello.h
+++ b/src/node_crypto_clienthello.h
@@ -24,8 +24,8 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
-#include <stddef.h>  // size_t
-#include <stdint.h>
+#include <cstddef>  // size_t
+#include <cstdint>
 
 namespace node {
 namespace crypto {
diff --git a/src/node_dtrace.cc b/src/node_dtrace.cc
index 0f33f59b338..59d1f9d143a 100644
--- a/src/node_dtrace.cc
+++ b/src/node_dtrace.cc
@@ -44,7 +44,7 @@
 
 #include "node_errors.h"
 
-#include <string.h>
+#include <cstring>
 
 namespace node {
 
diff --git a/src/node_errors.cc b/src/node_errors.cc
index a17012b5b37..17394c863cd 100644
--- a/src/node_errors.cc
+++ b/src/node_errors.cc
@@ -1,5 +1,5 @@
-#include <errno.h>
-#include <stdarg.h>
+#include <cerrno>
+#include <cstdarg>
 
 #include "node_errors.h"
 #include "node_internals.h"
diff --git a/src/node_file.cc b/src/node_file.cc
index 960fd052e88..96e0ba7e041 100644
--- a/src/node_file.cc
+++ b/src/node_file.cc
@@ -36,9 +36,9 @@
 #include <fcntl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#include <string.h>
-#include <errno.h>
-#include <limits.h>
+#include <cstring>
+#include <cerrno>
+#include <climits>
 
 #if defined(__MINGW32__) || defined(_MSC_VER)
 # include <io.h>
diff --git a/src/node_http2.h b/src/node_http2.h
index aa953667fac..9065718c60b 100644
--- a/src/node_http2.h
+++ b/src/node_http2.h
@@ -4,7 +4,7 @@
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
 // FIXME(joyeecheung): nghttp2.h needs stdint.h to compile on Windows
-#include <stdint.h>
+#include <cstdint>
 #include "nghttp2/nghttp2.h"
 
 #include "node_http2_state.h"
diff --git a/src/node_http_parser_impl.h b/src/node_http_parser_impl.h
index 16c0e77ae85..ae780d5371d 100644
--- a/src/node_http_parser_impl.h
+++ b/src/node_http_parser_impl.h
@@ -35,8 +35,8 @@
 #include "util-inl.h"
 #include "v8.h"
 
-#include <stdlib.h>  // free()
-#include <string.h>  // strdup(), strchr()
+#include <cstdlib>  // free()
+#include <cstring>  // strdup(), strchr()
 
 #include "http_parser_adaptor.h"
 
diff --git a/src/node_internals.h b/src/node_internals.h
index 82cf5713e95..166cfd9ea23 100644
--- a/src/node_internals.h
+++ b/src/node_internals.h
@@ -34,8 +34,8 @@
 #include "uv.h"
 #include "v8.h"
 
-#include <stdint.h>
-#include <stdlib.h>
+#include <cstdint>
+#include <cstdlib>
 
 #include <string>
 #include <vector>
diff --git a/src/node_main.cc b/src/node_main.cc
index 7107aea8c1a..e92c0df9429 100644
--- a/src/node_main.cc
+++ b/src/node_main.cc
@@ -20,7 +20,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #include "node.h"
-#include <stdio.h>
+#include <cstdio>
 
 #ifdef _WIN32
 #include <windows.h>
diff --git a/src/node_options.cc b/src/node_options.cc
index bdd39d5d71f..0d932200a95 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -1,4 +1,4 @@
-#include <errno.h>
+#include <cerrno>
 #include "env-inl.h"
 #include "node_binding.h"
 #include "node_options-inl.h"
diff --git a/src/node_os.cc b/src/node_os.cc
index 1d3680a6322..cbf2a304096 100644
--- a/src/node_os.cc
+++ b/src/node_os.cc
@@ -24,15 +24,15 @@
 #include "util.h"
 
 #include <array>
-#include <errno.h>
-#include <string.h>
+#include <cerrno>
+#include <cstring>
 
 #ifdef __MINGW32__
 # include <io.h>
 #endif  // __MINGW32__
 
 #ifdef __POSIX__
-# include <limits.h>        // PATH_MAX on Solaris.
+# include <climits>         // PATH_MAX on Solaris.
 # include <unistd.h>        // gethostname, sysconf
 #endif  // __POSIX__
 
diff --git a/src/node_process_events.cc b/src/node_process_events.cc
index ccc40b65753..440e67d4123 100644
--- a/src/node_process_events.cc
+++ b/src/node_process_events.cc
@@ -1,4 +1,4 @@
-#include <stdarg.h>
+#include <cstdarg>
 
 #include "env-inl.h"
 #include "node_process.h"
diff --git a/src/node_process_methods.cc b/src/node_process_methods.cc
index ca8a4358053..b46735bc791 100644
--- a/src/node_process_methods.cc
+++ b/src/node_process_methods.cc
@@ -15,8 +15,8 @@
 #include "inspector_io.h"
 #endif
 
-#include <limits.h>  // PATH_MAX
-#include <stdio.h>
+#include <climits>  // PATH_MAX
+#include <cstdio>
 
 #if defined(_MSC_VER)
 #include <direct.h>
diff --git a/src/node_process_object.cc b/src/node_process_object.cc
index 2f47b21f699..cbec233c27d 100644
--- a/src/node_process_object.cc
+++ b/src/node_process_object.cc
@@ -1,4 +1,4 @@
-#include <limits.h>  // PATH_MAX
+#include <climits>  // PATH_MAX
 
 #include "env-inl.h"
 #include "node_internals.h"
diff --git a/src/node_report.cc b/src/node_report.cc
index 8ca35cabb9c..a379f0621f9 100644
--- a/src/node_report.cc
+++ b/src/node_report.cc
@@ -27,12 +27,12 @@
 #endif
 #include <cxxabi.h>
 #include <dlfcn.h>
-#include <inttypes.h>
+#include <cinttypes>
 #endif
 
 #include <fcntl.h>
-#include <string.h>
-#include <time.h>
+#include <cstring>
+#include <ctime>
 #include <iomanip>
 
 #ifndef _MSC_VER
diff --git a/src/node_report.h b/src/node_report.h
index c83c52eb395..2aa55151d87 100644
--- a/src/node_report.h
+++ b/src/node_report.h
@@ -14,8 +14,8 @@
 #include <vector>
 #include "v8.h"
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <iomanip>
 #include <iostream>
 #include <sstream>
diff --git a/src/node_stat_watcher.cc b/src/node_stat_watcher.cc
index 9564a0a2b32..f673c4085e5 100644
--- a/src/node_stat_watcher.cc
+++ b/src/node_stat_watcher.cc
@@ -25,8 +25,8 @@
 #include "node_file.h"
 #include "util.h"
 
-#include <string.h>
-#include <stdlib.h>
+#include <cstring>
+#include <cstdlib>
 
 namespace node {
 
diff --git a/src/node_url.cc b/src/node_url.cc
index d7402c4d043..2070b713ac3 100644
--- a/src/node_url.cc
+++ b/src/node_url.cc
@@ -6,7 +6,7 @@
 
 #include <string>
 #include <vector>
-#include <stdio.h>
+#include <cstdio>
 #include <cmath>
 
 namespace node {
diff --git a/src/node_zlib.cc b/src/node_zlib.cc
index 639d7f87c5a..badac08449e 100644
--- a/src/node_zlib.cc
+++ b/src/node_zlib.cc
@@ -32,9 +32,9 @@
 #include "brotli/decode.h"
 #include "zlib.h"
 
-#include <errno.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cerrno>
+#include <cstdlib>
+#include <cstring>
 #include <sys/types.h>
 #include <atomic>
 
diff --git a/src/process_wrap.cc b/src/process_wrap.cc
index 37afaf8ff96..583851cdbb5 100644
--- a/src/process_wrap.cc
+++ b/src/process_wrap.cc
@@ -24,8 +24,8 @@
 #include "stream_wrap.h"
 #include "util-inl.h"
 
-#include <string.h>
-#include <stdlib.h>
+#include <cstring>
+#include <cstdlib>
 
 namespace node {
 
diff --git a/src/spawn_sync.cc b/src/spawn_sync.cc
index 749e628fbdf..6e5c3360cd4 100644
--- a/src/spawn_sync.cc
+++ b/src/spawn_sync.cc
@@ -25,7 +25,7 @@
 #include "node_internals.h"
 #include "string_bytes.h"
 
-#include <string.h>
+#include <cstring>
 
 
 namespace node {
diff --git a/src/stream_base.cc b/src/stream_base.cc
index ebd9beb984e..24210e1e260 100644
--- a/src/stream_base.cc
+++ b/src/stream_base.cc
@@ -10,7 +10,7 @@
 #include "util-inl.h"
 #include "v8.h"
 
-#include <limits.h>  // INT_MAX
+#include <climits>  // INT_MAX
 
 namespace node {
 
diff --git a/src/stream_wrap.cc b/src/stream_wrap.cc
index d126f90eef8..3247a604b43 100644
--- a/src/stream_wrap.cc
+++ b/src/stream_wrap.cc
@@ -31,8 +31,8 @@
 #include "udp_wrap.h"
 #include "util-inl.h"
 
-#include <string.h>  // memcpy()
-#include <limits.h>  // INT_MAX
+#include <cstring>  // memcpy()
+#include <climits>  // INT_MAX
 
 
 namespace node {
diff --git a/src/string_bytes.cc b/src/string_bytes.cc
index 53bb95d80da..041868cb1e7 100644
--- a/src/string_bytes.cc
+++ b/src/string_bytes.cc
@@ -27,8 +27,8 @@
 #include "node_errors.h"
 #include "util.h"
 
-#include <limits.h>
-#include <string.h>  // memcpy
+#include <climits>
+#include <cstring>  // memcpy
 
 #include <algorithm>
 #include <vector>
diff --git a/src/string_search.h b/src/string_search.h
index 95c746ea89e..3968c8c8690 100644
--- a/src/string_search.h
+++ b/src/string_search.h
@@ -9,7 +9,7 @@
 
 #include "util.h"
 
-#include <string.h>
+#include <cstring>
 #include <algorithm>
 
 namespace node {
diff --git a/src/tcp_wrap.cc b/src/tcp_wrap.cc
index cb6e6340067..43c6ea5958f 100644
--- a/src/tcp_wrap.cc
+++ b/src/tcp_wrap.cc
@@ -31,7 +31,7 @@
 #include "stream_wrap.h"
 #include "util-inl.h"
 
-#include <stdlib.h>
+#include <cstdlib>
 
 
 namespace node {
diff --git a/src/timers.cc b/src/timers.cc
index f80e9e6be4d..b11df62be21 100644
--- a/src/timers.cc
+++ b/src/timers.cc
@@ -2,7 +2,7 @@
 #include "util.h"
 #include "v8.h"
 
-#include <stdint.h>
+#include <cstdint>
 
 namespace node {
 namespace {
diff --git a/src/tracing/node_trace_writer.cc b/src/tracing/node_trace_writer.cc
index b93688cc958..3b07504acc4 100644
--- a/src/tracing/node_trace_writer.cc
+++ b/src/tracing/node_trace_writer.cc
@@ -1,6 +1,6 @@
 #include "tracing/node_trace_writer.h"
 
-#include <string.h>
+#include <cstring>
 #include <fcntl.h>
 
 #include "util-inl.h"
diff --git a/src/tracing/traced_value.cc b/src/tracing/traced_value.cc
index b2a1badad12..3eb21a11c93 100644
--- a/src/tracing/traced_value.cc
+++ b/src/tracing/traced_value.cc
@@ -6,7 +6,7 @@
 
 #include <cmath>
 #include <sstream>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 
 #if defined(NODE_HAVE_I18N_SUPPORT)
diff --git a/src/tracing/traced_value.h b/src/tracing/traced_value.h
index 7507978408f..955d62dfe6c 100644
--- a/src/tracing/traced_value.h
+++ b/src/tracing/traced_value.h
@@ -9,7 +9,7 @@
 #include "util.h"
 #include "v8.h"
 
-#include <stddef.h>
+#include <cstddef>
 #include <memory>
 #include <string>
 
diff --git a/src/util.cc b/src/util.cc
index 81070c239d8..3cdc222a960 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -19,7 +19,7 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-#include <stdio.h>
+#include <cstdio>
 #include <sstream>
 #include "node_buffer.h"
 #include "node_errors.h"
diff --git a/src/util.h b/src/util.h
index 312f91e68e8..4cd04dc6af9 100644
--- a/src/util.h
+++ b/src/util.h
@@ -27,12 +27,12 @@
 #include "node_persistent.h"
 #include "v8.h"
 
-#include <assert.h>
-#include <signal.h>
-#include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cassert>
+#include <csignal>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 #include <functional>  // std::function
 #include <limits>
diff --git a/test/cctest/node_test_fixture.h b/test/cctest/node_test_fixture.h
index e34601af99a..f7ecb9cdea7 100644
--- a/test/cctest/node_test_fixture.h
+++ b/test/cctest/node_test_fixture.h
@@ -1,7 +1,7 @@
 #ifndef TEST_CCTEST_NODE_TEST_FIXTURE_H_
 #define TEST_CCTEST_NODE_TEST_FIXTURE_H_
 
-#include <stdlib.h>
+#include <cstdlib>
 #include "gtest/gtest.h"
 #include "node.h"
 #include "node_platform.h"
diff --git a/test/cctest/test_base64.cc b/test/cctest/test_base64.cc
index fbdb969b4cb..5e39a1052bc 100644
--- a/test/cctest/test_base64.cc
+++ b/test/cctest/test_base64.cc
@@ -1,7 +1,7 @@
 #include "base64.h"
 
-#include <stddef.h>
-#include <string.h>
+#include <cstddef>
+#include <cstring>
 
 #include "gtest/gtest.h"
 
diff --git a/test/cctest/test_traced_value.cc b/test/cctest/test_traced_value.cc
index 5329c78446c..fa938c881ef 100644
--- a/test/cctest/test_traced_value.cc
+++ b/test/cctest/test_traced_value.cc
@@ -1,8 +1,8 @@
 #include "tracing/traced_value.h"
 
-#include <math.h>
-#include <stddef.h>
-#include <string.h>
+#include <cmath>
+#include <cstddef>
+#include <cstring>
 
 #include "gtest/gtest.h"
 
diff --git a/tools/icu/iculslocs.cc b/tools/icu/iculslocs.cc
index f086724a848..8b1fa527c2c 100644
--- a/tools/icu/iculslocs.cc
+++ b/tools/icu/iculslocs.cc
@@ -50,12 +50,12 @@ Japanese, it doesn't *claim* to have Japanese.
 
 */
 
-#include "string.h"
+#include <cstring>
 #include "charstr.h"  // ICU internal header
 #include <unicode/ures.h>
 #include <unicode/udata.h>
 #include <unicode/putil.h>
-#include <stdio.h>
+#include <cstdio>
 
 const char* PROG = "iculslocs";
 const char* NAME = U_ICUDATA_NAME;  // assume ICU data