--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -150,30 +150,31 @@ case "$target" in
 *-mingw*)
     if test "$GCC" != "yes"; then
         # Check to see if we are really running in a msvc environemnt
         _WIN32_MSVC=1
 
         # Make sure compilers are valid
         CFLAGS="$CFLAGS -TC -nologo"
         CXXFLAGS="$CXXFLAGS -TP -nologo"
+        if test -z "$CLANG_CL"; then
+            CFLAGS="$CFLAGS -utf-8"
+            CXXFLAGS="$CXXFLAGS -utf-8"
+        fi
         # MSVC warning C4345 warns of newly conformant behavior as of VS2003.
         # MSVC warning C4351 warns of newly conformant behavior as of VS2005.
         # MSVC warning C4800 warns when a value is implicitly cast to bool,
         # because this also forces narrowing to a single byte, which can be a
         # perf hit.  But this matters so little in practice (and often we want
         # that behavior) that it's better to turn it off.
         # _CRT_SECURE_NO_WARNINGS disables warnings about using MSVC-specific
         # secure CRT functions.
-        # MSVC warning C4819 warns some UTF-8 characters (e.g. copyright sign)
-        # on non-Western system locales even if it is in a comment.
         # MSVC warning wd4595 warns non-member operator new or delete functions
         # may not be declared inline, as of VS2015 Update 2.
-        CFLAGS="$CFLAGS -wd4819"
-        CXXFLAGS="$CXXFLAGS -wd4345 -wd4351 -wd4800 -wd4819 -wd4595 -D_CRT_SECURE_NO_WARNINGS"
+        CXXFLAGS="$CXXFLAGS -wd4345 -wd4351 -wd4800 -wd4595 -D_CRT_SECURE_NO_WARNINGS"
         AC_LANG_SAVE
         AC_LANG_C
         AC_TRY_COMPILE([#include <stdio.h>],
             [ printf("Hello World\n"); ],,
             AC_MSG_ERROR([\$(CC) test failed.  You must have MS VC++ in your path to build.]) )
 
         AC_LANG_CPLUSPLUS
         AC_TRY_COMPILE([#include <new.h>],

--- a/old-configure.in
+++ b/old-configure.in
@@ -1031,16 +1031,20 @@ case "$target" in
         WIN32_CONSOLE_EXE_LDFLAGS=-SUBSYSTEM:CONSOLE,$WIN32_SUBSYSTEM_VERSION
         WIN32_GUI_EXE_LDFLAGS=-SUBSYSTEM:WINDOWS,$WIN32_SUBSYSTEM_VERSION
         DSO_LDOPTS=-SUBSYSTEM:WINDOWS,$WIN32_SUBSYSTEM_VERSION
         _USE_CPP_INCLUDE_FLAG=1
         _DEFINES_CFLAGS='-FI $(topobjdir)/mozilla-config.h -DMOZILLA_CLIENT'
         _DEFINES_CXXFLAGS='-FI $(topobjdir)/mozilla-config.h -DMOZILLA_CLIENT'
         CFLAGS="$CFLAGS -W3 -Gy -Zc:inline"
         CXXFLAGS="$CXXFLAGS -W3 -Gy -Zc:inline"
+        if test -z "$CLANG_CL"; then
+            CFLAGS="$CFLAGS -utf-8"
+            CXXFLAGS="$CXXFLAGS -utf-8"
+        fi
         if test "$CPU_ARCH" = "x86"; then
             dnl VS2012+ defaults to -arch:SSE2. We want to target nothing
             dnl more recent, so set that explicitly here unless another
             dnl target arch has already been set.
             if test -z `echo $CFLAGS | grep -i [-/]arch:`; then
               CFLAGS="$CFLAGS -arch:SSE2"
             fi
             if test -z `echo $CXXFLAGS | grep -i [-/]arch:`; then
@@ -1077,22 +1081,20 @@ case "$target" in
         # to 32-bit integer types on 64-bit platforms.  Since this is virtually
         # the same thing as C4244, we disable C4267, too.
         # MSVC warning C4345 warns of newly conformant behavior as of VS2003.
         # MSVC warning C4351 warns of newly conformant behavior as of VS2005.
         # MSVC warning C4800 warns when a value is implicitly cast to bool,
         # because this also forces narrowing to a single byte, which can be a
         # perf hit.  But this matters so little in practice (and often we want
         # that behavior) that it's better to turn it off.
-        # MSVC warning C4819 warns some UTF-8 characters (e.g. copyright sign)
-        # on non-Western system locales even if it is in a comment.
         # MSVC warning wd4595 warns non-member operator new or delete functions
         # may not be declared inline, as of VS2015 Update 2.
-        CFLAGS="$CFLAGS -wd4244 -wd4267 -wd4819"
-        CXXFLAGS="$CXXFLAGS -wd4251 -wd4244 -wd4267 -wd4345 -wd4351 -wd4800 -wd4819 -wd4595"
+        CFLAGS="$CFLAGS -wd4244 -wd4267"
+        CXXFLAGS="$CXXFLAGS -wd4251 -wd4244 -wd4267 -wd4345 -wd4351 -wd4800 -wd4595"
         if test -n "$CLANG_CL"; then
             # XXX We should combine some of these with our generic GCC-style
             # warning checks.
             #
             # Suppress the clang-cl warning for the inline 'new' and 'delete' in mozalloc
             CXXFLAGS="$CXXFLAGS -Wno-inline-new-delete"
             # We use offsetof on non-POD objects all the time.
             # We also suppress this warning on other platforms.