diff --git a/src/inspector/node_string.cc b/src/inspector/node_string.cc
index 0d403c66f0197b..4cb8b573cc1312 100644
--- a/src/inspector/node_string.cc
+++ b/src/inspector/node_string.cc
@@ -71,14 +71,14 @@ String StringViewToUtf8(v8_inspector::StringView view) {
 
 String fromDouble(double d) {
   std::ostringstream stream;
-  stream.imbue(std::locale("C"));  // Ignore locale
+  stream.imbue(std::locale::classic());  // Ignore current locale
   stream << d;
   return stream.str();
 }
 
 double toDouble(const char* buffer, size_t length, bool* ok) {
   std::istringstream stream(std::string(buffer, length));
-  stream.imbue(std::locale("C"));  // Ignore locale
+  stream.imbue(std::locale::classic());  // Ignore current locale
   double d;
   stream >> d;
   *ok = !stream.fail();
diff --git a/src/tracing/traced_value.cc b/src/tracing/traced_value.cc
index dfc11658e7e4e3..662b0357a19305 100644
--- a/src/tracing/traced_value.cc
+++ b/src/tracing/traced_value.cc
@@ -94,7 +94,7 @@ std::string DoubleToCString(double v) {
     default:
       // This is a far less sophisticated version than the one used inside v8.
       std::ostringstream stream;
-      stream.imbue(std::locale("C"));  // Ignore locale
+      stream.imbue(std::locale::classic());  // Ignore current locale
       stream << v;
       return stream.str();
   }
diff --git a/src/util-inl.h b/src/util-inl.h
index 00a9f836e46a40..517da707170586 100644
--- a/src/util-inl.h
+++ b/src/util-inl.h
@@ -26,6 +26,7 @@
 
 #include <cmath>
 #include <cstring>
+#include <locale>
 #include "util.h"
 
 // These are defined by <sys/byteorder.h> or <netinet/in.h> on some systems.
@@ -274,7 +275,7 @@ void SwapBytes64(char* data, size_t nbytes) {
 }
 
 char ToLower(char c) {
-  return c >= 'A' && c <= 'Z' ? c + ('a' - 'A') : c;
+  return std::tolower(c, std::locale::classic());
 }
 
 std::string ToLower(const std::string& in) {
@@ -285,7 +286,7 @@ std::string ToLower(const std::string& in) {
 }
 
 char ToUpper(char c) {
-  return c >= 'a' && c <= 'z' ? (c - 'a') + 'A' : c;
+  return std::toupper(c, std::locale::classic());
 }
 
 std::string ToUpper(const std::string& in) {