--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -527,18 +527,16 @@ case "$target" in
 
 *-mingw*)
     DSO_CFLAGS=
     DSO_PIC_CFLAGS=
     if test -n "$GNU_CC" -o -n "$CLANG_CC"; then
         CC="$CC -mwindows"
         CXX="$CXX -mwindows"
         CPP="$CPP -mwindows"
-        CFLAGS="$CFLAGS -mms-bitfields"
-        CXXFLAGS="$CXXFLAGS -mms-bitfields"
         DSO_LDOPTS='-shared'
         # Use temp file for windres (bug 213281)
         RCFLAGS='-O coff --use-temp-file'
         # mingw doesn't require kernel32, user32, and advapi32 explicitly
         LIBS="$LIBS -lusp10 -lgdi32 -lwinmm -lwsock32"
         MOZ_FIX_LINK_PATHS=
 
         if test -z "$CLANG_CC"; then

--- a/old-configure.in
+++ b/old-configure.in
@@ -646,18 +646,16 @@ case "$target" in
     DSO_CFLAGS=
     DSO_PIC_CFLAGS=
     # certain versions of cygwin's makedepend barf on the
     # #include <string> vs -I./dist/include/string issue so don't use it
     if test -n "$GNU_CC" -o -n "$CLANG_CC"; then
         CC="$CC -mwindows"
         CXX="$CXX -mwindows"
         CPP="$CPP -mwindows"
-        CFLAGS="$CFLAGS -mms-bitfields"
-        CXXFLAGS="$CXXFLAGS -mms-bitfields"
         DSO_LDOPTS='-shared'
         # Use temp file for windres (bug 213281)
         RCFLAGS='-O coff --use-temp-file'
         # mingw doesn't require kernel32, user32, and advapi32 explicitly
         LIBS="$LIBS -luuid -lusp10 -lgdi32 -lwinmm -lwsock32 -luserenv -lsecur32"
         MOZ_FIX_LINK_PATHS=
 
         MOZ_OPTIMIZE_FLAGS="-O2"