diff --git a/gcc/ada/adaint.c b/gcc/ada/adaint.c
index 595abf87d65..c836566803d 100644
--- a/gcc/ada/adaint.c
+++ b/gcc/ada/adaint.c
@@ -279,6 +279,12 @@ char __gnat_dir_separator = DIR_SEPARATOR;
 
 char __gnat_path_separator = PATH_SEPARATOR;
 
+#ifdef __DJGPP__
+int __gnat_is_djgpp = 1;
+#else
+int __gnat_is_djgpp = 0;
+#endif
+
 /* The GNAT_LIBRARY_TEMPLATE contains a list of expressions that define
    the base filenames that libraries specified with -lsomelib options
    may have. This is used by GNATMAKE to check whether an executable
@@ -578,7 +584,11 @@ __gnat_try_lock (char *dir, char *file)
 int
 __gnat_get_maximum_file_name_length (void)
 {
+#if defined (__DJGPP__)
+  return (_use_lfn(".")) ? -1 : 8;
+#else
   return -1;
+#endif
 }
 
 /* Return nonzero if file names are case sensitive.  */
diff --git a/gcc/ada/gcc-interface/Make-lang.in b/gcc/ada/gcc-interface/Make-lang.in
index acbe2b877ca..4962b36ee2e 100644
--- a/gcc/ada/gcc-interface/Make-lang.in
+++ b/gcc/ada/gcc-interface/Make-lang.in
@@ -1077,7 +1077,7 @@ ada/generated/gnatvsn.ads: ada/gnatvsn.ads BASE-VER ada/GNAT_DATE
 	s=`cat $(srcdir)/BASE-VER | sed -e "s/\([0-9]*\)\.\([0-9]*\)\..*/-\1\2/g"`; \
 	d=`if test -f $(srcdir)/ada/GNAT_DATE; then \
            cat $(srcdir)/ada/GNAT_DATE; else date +%Y%m%d; fi`; \
-	cat $< | sed -e "/Version/s/(\([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]\).*)/($$d$$s)/g" >$@
+	cat $< | sed -e "/Version/s/(\([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]\).*)/($$d$$s)/g" | tr -d \\\015 >$@
 
 ada/gnatvsn.o : ada/gnatvsn.adb ada/generated/gnatvsn.ads
 	$(CC) -c $(ALL_ADAFLAGS) -Iada/generated -I../ada/generated $(ADA_INCLUDES) $< $(ADA_OUTPUT_OPTION)
diff --git a/gcc/ada/libgnarl/s-taprop__dummy.adb b/gcc/ada/libgnarl/s-taprop__dummy.adb
index bd6387d821c..0cb49e3f553 100644
--- a/gcc/ada/libgnarl/s-taprop__dummy.adb
+++ b/gcc/ada/libgnarl/s-taprop__dummy.adb
@@ -41,7 +41,7 @@ pragma Polling (Off);
 package body System.Task_Primitives.Operations is
 
    use System.Tasking;
-   use System.Parameters;
+--   use System.Parameters;
 
    pragma Warnings (Off);
    --  Turn off warnings since so many unreferenced parameters
diff --git a/gcc/ada/libgnat/s-os_lib.adb b/gcc/ada/libgnat/s-os_lib.adb
index 258cd64d312..3943a15458b 100644
--- a/gcc/ada/libgnat/s-os_lib.adb
+++ b/gcc/ada/libgnat/s-os_lib.adb
@@ -71,7 +71,7 @@ package body System.OS_Lib is
 
    --  The following are used by Create_Temp_File
 
-   First_Temp_File_Name : constant String := "GNAT-TEMP-000000.TMP";
+   First_Temp_File_Name : constant String := "GA000000.TMP";
    --  Used to initialize Current_Temp_File_Name and Temp_File_Name_Last_Digit
 
    Current_Temp_File_Name : String := First_Temp_File_Name;
@@ -2259,9 +2259,10 @@ package body System.OS_Lib is
       --    * Check the drive letter
       --    * Remove all double-quotes
 
-      if On_Windows then
+      if On_Windows
+        and then Is_Djgpp = 0
+      then
          --  Replace all '/' by '\'
-
          for Index in 1 .. End_Path loop
             if Path_Buffer (Index) = '/' then
                Path_Buffer (Index) := Directory_Separator;
diff --git a/gcc/ada/libgnat/s-os_lib.ads b/gcc/ada/libgnat/s-os_lib.ads
index 99406e9a77d..a35507806a6 100644
--- a/gcc/ada/libgnat/s-os_lib.ads
+++ b/gcc/ada/libgnat/s-os_lib.ads
@@ -1091,9 +1091,12 @@ package System.OS_Lib is
    Path_Separator : constant Character;
    --  The character to separate paths in an environment variable value
 
+   Is_Djgpp : constant Integer;
+
 private
    pragma Import (C, Path_Separator, "__gnat_path_separator");
    pragma Import (C, Directory_Separator, "__gnat_dir_separator");
+   pragma Import (C, Is_Djgpp, "__gnat_is_djgpp");
    pragma Import (C, Current_Time, "__gnat_current_time");
    pragma Import (C, Current_Process_Id, "__gnat_current_process_id");
 
diff --git a/gcc/collect2.c b/gcc/collect2.c
index f8a5ce45994..2c3a612d49f 100644
--- a/gcc/collect2.c
+++ b/gcc/collect2.c
@@ -1180,18 +1180,27 @@ main (int argc, char **argv)
   *ld1++ = *ld2++ = ld_file_name;
 
   /* Make temp file names.  */
+
+#ifdef __DJGPP__
+#define CDTOR_C_NAME ".ctc"
+#define CDTOR_O_NAME ".cto"
+#else
+#define CDTOR_C_NAME ".cdtor.c"
+#define CDTOR_O_NAME ".cdtor.o"
+#endif
+
   if (save_temps)
     {
-      c_file = concat (output_file, ".cdtor.c", NULL);
-      o_file = concat (output_file, ".cdtor.o", NULL);
+      c_file = concat (output_file, CDTOR_C_NAME, NULL);
+      o_file = concat (output_file, CDTOR_O_NAME, NULL);
 #ifdef COLLECT_EXPORT_LIST
       export_file = concat (output_file, ".x", NULL);
 #endif
     }
   else
     {
-      c_file = make_temp_file (".cdtor.c");
-      o_file = make_temp_file (".cdtor.o");
+      c_file = make_temp_file (CDTOR_C_NAME);
+      o_file = make_temp_file (CDTOR_O_NAME);
 #ifdef COLLECT_EXPORT_LIST
       export_file = make_temp_file (".x");
 #endif
diff --git a/gcc/config/i386/djgpp.c b/gcc/config/i386/djgpp.c
index ba6c2d4d3a4..88cf1e6506e 100644
--- a/gcc/config/i386/djgpp.c
+++ b/gcc/config/i386/djgpp.c
@@ -36,6 +36,8 @@ i386_djgpp_asm_named_section(const char *name, unsigned int flags,
     *f++ = 'w';
   if (flags & SECTION_CODE)
     *f++ = 'x';
+  if (flags & SECTION_BSS)
+    *f++ = 'b';
 
   /* LTO sections need 1-byte alignment to avoid confusing the
      zlib decompression algorithm with trailing zero pad bytes.  */
diff --git a/gcc/config/i386/xm-djgpp.h b/gcc/config/i386/xm-djgpp.h
index 299ef0a4810..a376a3f9146 100644
--- a/gcc/config/i386/xm-djgpp.h
+++ b/gcc/config/i386/xm-djgpp.h
@@ -30,6 +30,8 @@ along with GCC; see the file COPYING3.  If not see
 #undef NATIVE_SYSTEM_HEADER_DIR
 #define NATIVE_SYSTEM_HEADER_DIR "/dev/env/DJDIR/include/"
 
+//#undef PREFIX_INCLUDE_DIR
+
 /* Search for as.exe and ld.exe in DJGPP's binary directory.  */
 #undef MD_EXEC_PREFIX
 #define MD_EXEC_PREFIX "/dev/env/DJDIR/bin/"
@@ -107,6 +109,11 @@ along with GCC; see the file COPYING3.  If not see
       (PATH) = xstrdup (fixed_path);		\
     }
 
+/* Rename libstdc++ to libstdcxx as the first name is not valid for DOS */
+#define LIBSTDCXX "stdcxx"
+#define LIBSTDCXX_PROFILE "stdcxx"
+#define LIBSTDCXX_STATIC "stdcxx"
+
 #undef MAX_OFILE_ALIGNMENT
 #define MAX_OFILE_ALIGNMENT 128
 
diff --git a/gcc/gcov-tool.c b/gcc/gcov-tool.c
index f8f1cb5d29b..bd26e1f2443 100644
--- a/gcc/gcov-tool.c
+++ b/gcc/gcov-tool.c
@@ -56,11 +56,18 @@ static bool verbose;
 
 /* Remove file NAME if it has a gcda suffix. */
 
+#ifdef __DJGPP__
+static int
+unlink_gcda_file (const char *name,
+                  struct stat *status ATTRIBUTE_UNUSED,
+                  int type ATTRIBUTE_UNUSED)
+#else
 static int
 unlink_gcda_file (const char *name,
                   const struct stat *status ATTRIBUTE_UNUSED,
                   int type ATTRIBUTE_UNUSED,
                   struct FTW *ftwbuf ATTRIBUTE_UNUSED)
+#endif
 {
   int ret = 0;
   int len = strlen (name);
@@ -82,7 +89,11 @@ static int
 unlink_profile_dir (const char *path ATTRIBUTE_UNUSED)
 {
 #if HAVE_FTW_H
+#ifdef __DJGPP__
+    return ftw(path, unlink_gcda_file, 64);
+#else
     return nftw(path, unlink_gcda_file, 64, FTW_DEPTH | FTW_PHYS);
+#endif
 #else
     return -1;
 #endif
diff --git a/gcc/ggc-common.c b/gcc/ggc-common.c
index 0d528cf455c..c6d4134bb36 100644
--- a/gcc/ggc-common.c
+++ b/gcc/ggc-common.c
@@ -31,6 +31,12 @@ along with GCC; see the file COPYING3.  If not see
 #include "plugin.h"
 #include "options.h"
 
+#ifdef __DJGPP__
+extern "C" {
+#include <libc/malldbg.h>
+}
+#endif
+
 /* When set, ggc_collect will do collection.  */
 bool ggc_force_collect;
 
diff --git a/gcc/ginclude/float.h b/gcc/ginclude/float.h
index 9c4b0385568..986639a3bc9 100644
--- a/gcc/ginclude/float.h
+++ b/gcc/ginclude/float.h
@@ -25,6 +25,10 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  * ISO C Standard:  5.2.4.2.2  Characteristics of floating types <float.h>
  */
 
+#ifdef __DJGPP__
+#include_next <float.h>
+#endif
+
 #ifndef _FLOAT_H___
 #define _FLOAT_H___
 
diff --git a/include/libiberty.h b/include/libiberty.h
index 141cb886a85..e2462fc3332 100644
--- a/include/libiberty.h
+++ b/include/libiberty.h
@@ -108,6 +108,7 @@ extern int countargv (char * const *);
 #if defined (__GNU_LIBRARY__ ) || defined (__linux__) \
  || defined (__FreeBSD__) || defined (__OpenBSD__) || defined (__NetBSD__) \
  || defined (__CYGWIN__) || defined (__CYGWIN32__) || defined (__MINGW32__) \
+ || defined (__DJGPP__) \
  || defined (__DragonFly__) || defined (HAVE_DECL_BASENAME) 
 extern char *basename (const char *) ATTRIBUTE_RETURNS_NONNULL ATTRIBUTE_NONNULL(1);
 #else
diff --git a/libcpp/files.c b/libcpp/files.c
index 260e787c329..d8a63d43bea 100644
--- a/libcpp/files.c
+++ b/libcpp/files.c
@@ -747,6 +747,10 @@ read_file_guts (cpp_reader *pfile, _cpp_file *file, location_t loc)
     cpp_error_at (pfile, CPP_DL_WARNING, loc,
 	       "%s is shorter than expected", file->path);
 
+/* For DOS we should handle DOS EOF character (0x1A, ^Z). It is
+   only done if it is really the last character of the file  */
+  if (total>0 && buf[total-1]==0x1A) total--;
+
   file->buffer = _cpp_convert_input (pfile,
 				     CPP_OPTION (pfile, input_charset),
 				     buf, size + 16, total,
diff --git a/libcpp/lex.c b/libcpp/lex.c
index 665297af776..90e58ff26de 100644
--- a/libcpp/lex.c
+++ b/libcpp/lex.c
@@ -502,6 +502,13 @@ init_vectorized_lexer (void)
   search_line_fast_type impl = search_line_acc_char;
   int minimum = 0;
 
+// [FIXME][DJGPP] Using SSE here causes preprocessor to randomly
+// [FIXME][DJGPP] fail when run under Windows 10 32 bit (and maybe
+// [FIXME][DJGPP] some other systems (I have observed similar
+// [FIXME][DJGPP] behavior earlier with DJGPP v2.03p2 under Windows
+// [FIXME][DJGPP] Vista
+#ifndef __DJGPP__
+
 #if defined(__SSE4_2__)
   minimum = 3;
 #elif defined(__SSE2__)
@@ -528,6 +535,8 @@ init_vectorized_lexer (void)
 	impl = search_line_mmx;
     }
 
+#endif // __DJGPP__
+
   search_line_fast = impl;
 }
 
diff --git a/libcpp/macro.c b/libcpp/macro.c
index 2573f316bf5..9f3b3e7f8de 100644
--- a/libcpp/macro.c
+++ b/libcpp/macro.c
@@ -612,17 +612,22 @@ _cpp_builtin_macro_text (cpp_reader *pfile, cpp_hashnode *node,
 	      && pfile->cb.get_source_date_epoch != NULL)
 	    pfile->source_date_epoch = pfile->cb.get_source_date_epoch (pfile);
 
-	  if (pfile->source_date_epoch >= (time_t) 0)
-	    tb = gmtime (&pfile->source_date_epoch);
-	  else
-	    {
-	      /* (time_t) -1 is a legitimate value for "number of seconds
-		 since the Epoch", so we have to do a little dance to
-		 distinguish that from a genuine error.  */
-	      errno = 0;
-	      tt = time (NULL);
-	      if (tt != (time_t)-1 || errno == 0)
-		tb = localtime (&tt);
+          switch (pfile->source_date_epoch)
+            {
+               default:
+                   tb = gmtime (&pfile->source_date_epoch);
+                   break;
+
+               case (time_t) -1:
+               case (time_t) -2:
+	           /* (time_t) -1 is a legitimate value for "number of seconds
+		      since the Epoch", so we have to do a little dance to
+		      distinguish that from a genuine error.  */
+	           errno = 0;
+	           tt = time (NULL);
+	           if (tt != (time_t)-1 || errno == 0)
+		       tb = localtime (&tt);
+                   break;
 	    }
 
 	  if (tb)
diff --git a/libffi/src/x86/sysv.S b/libffi/src/x86/sysv.S
index 78f245bda07..1ae18b248a7 100644
--- a/libffi/src/x86/sysv.S
+++ b/libffi/src/x86/sysv.S
@@ -822,7 +822,7 @@ ENDF(C(__x86.get_pc_thunk.dx))
 #ifdef __APPLE__
 .section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support
 EHFrame0:
-#elif defined(X86_WIN32)
+#elif defined(X86_WIN32) || defined(__DJGPP__)
 .section .eh_frame,"r"
 #elif defined(HAVE_AS_X86_64_UNWIND_SECTION_TYPE)
 .section .eh_frame,EH_FRAME_FLAGS,@unwind
diff --git a/libgcc/libgcov-util.c b/libgcc/libgcov-util.c
index fff54c6a3f6..c4879c6bf99 100644
--- a/libgcc/libgcov-util.c
+++ b/libgcc/libgcov-util.c
@@ -390,7 +390,11 @@ read_gcda_file (const char *filename)
 
 static int
 ftw_read_file (const char *filename,
+#ifdef __DJGPP__
+               struct stat *status ATTRIBUTE_UNUSED,
+#else
                const struct stat *status ATTRIBUTE_UNUSED,
+#endif
                int type)
 {
   int filename_len;
diff --git a/libgfortran/intrinsics/chmod.c b/libgfortran/intrinsics/chmod.c
index 7377834be69..7480d3ce17e 100644
--- a/libgfortran/intrinsics/chmod.c
+++ b/libgfortran/intrinsics/chmod.c
@@ -442,7 +442,7 @@ clause_done:
 	if ((ugo[2] || honor_umask) && !rwxXstugo[8])
 	  file_mode = (file_mode & ~(S_IROTH | S_IWOTH | S_IXOTH))
 		      | (new_mode & (S_IROTH | S_IWOTH | S_IXOTH));
-#ifndef __VXWORKS__
+#if !defined(__VXWORKS__) && !defined(__DJGPP__)
 	if (is_dir && rwxXstugo[5])
 	  file_mode |= S_ISVTX;
 	else if (!is_dir)
@@ -454,7 +454,7 @@ clause_done:
       {
 	/* Clear '-'.  */
 	file_mode &= ~new_mode;
-#if !defined( __MINGW32__) && !defined (__VXWORKS__)
+#if !defined( __MINGW32__) && !defined (__VXWORKS__) && !defined(__DJGPP__)
 	if (rwxXstugo[5] || !is_dir)
 	  file_mode &= ~S_ISVTX;
 #endif
@@ -462,7 +462,7 @@ clause_done:
     else if (set_mode == 3)
       {
 	file_mode |= new_mode;
-#if !defined (__MINGW32__) && !defined (__VXWORKS__)
+#if !defined (__MINGW32__) && !defined (__VXWORKS__) && !defined(__DJGPP__)
 	if (rwxXstugo[5] && is_dir)
 	  file_mode |= S_ISVTX;
 	else if (!is_dir)
diff --git a/libgfortran/intrinsics/execute_command_line.c b/libgfortran/intrinsics/execute_command_line.c
index 6d7b8fc658e..ac7e0054c2f 100644
--- a/libgfortran/intrinsics/execute_command_line.c
+++ b/libgfortran/intrinsics/execute_command_line.c
@@ -98,7 +98,7 @@ execute_command_line (const char *command, bool wait, int *exitstat,
 
       set_cmdstat (cmdstat, EXEC_NOERROR);
 
-#if defined(HAVE_SIGACTION) && defined(HAVE_WAITPID)
+#if defined(HAVE_SIGACTION) && defined(HAVE_WAITPID) && !defined(__DJGPP__)
       static bool sig_init_saved;
       bool sig_init = __atomic_load_n (&sig_init_saved, __ATOMIC_RELAXED);
       if (!sig_init)
diff --git a/libgfortran/io/unix.c b/libgfortran/io/unix.c
index 563c7cb64cc..e8d681735ba 100644
--- a/libgfortran/io/unix.c
+++ b/libgfortran/io/unix.c
@@ -221,6 +221,9 @@ typedef struct
 }
 unix_stream;
 
+#ifdef __DJGPP__
+#include <io.h>
+#endif
 
 /* fix_fd()-- Given a file descriptor, make sure it is not one of the
    standard descriptors, returning a non-standard descriptor.  If the
@@ -1222,8 +1225,13 @@ tempfile_open (const char *tempdir, char **fname)
   char *template = xmalloc (tempdirlen + 23);
 
 #ifdef HAVE_MKSTEMP
+#ifdef __DJGPP__
+  /* Default filename is too long for DOS */
+  snprintf (template, tempdirlen + 23, "%s/gfXXXXXX", tempdir);
+#else
   snprintf (template, tempdirlen + 23, "%s%sgfortrantmpXXXXXX", 
 	    tempdir, slash);
+#endif
 
 #ifdef HAVE_UMASK
   /* Temporarily set the umask such that the file has 0600 permissions.  */
@@ -1589,6 +1597,13 @@ open_external (st_parameter_open *opp, unit_flags *flags)
     return NULL;
   fd = fix_fd (fd);
 
+#ifdef __DJGPP__
+  if (flags->form == FORM_UNFORMATTED)
+    {
+      setmode (fd, O_BINARY);
+    }
+#endif
+
   if (open_share (opp, fd, flags) < 0)
     return NULL;
 
diff --git a/libiberty/make-relative-prefix.c b/libiberty/make-relative-prefix.c
index e3f9f920df4..836de31c156 100644
--- a/libiberty/make-relative-prefix.c
+++ b/libiberty/make-relative-prefix.c
@@ -65,6 +65,7 @@ relative prefix can be found, return @code{NULL}.
 
 #include "ansidecl.h"
 #include "libiberty.h"
+#include "filenames.h"
 
 #ifndef R_OK
 #define R_OK 4
@@ -340,7 +341,7 @@ make_relative_prefix_1 (const char *progname, const char *bin_prefix,
     {
       for (i = 0; i < bin_num; i++)
 	{
-	  if (strcmp (prog_dirs[i], bin_dirs[i]) != 0)
+	  if (FILENAME_CMP (prog_dirs[i], bin_dirs[i]) != 0)
 	    break;
 	}
 
@@ -356,7 +357,7 @@ make_relative_prefix_1 (const char *progname, const char *bin_prefix,
   n = (prefix_num < bin_num) ? prefix_num : bin_num;
   for (common = 0; common < n; common++)
     {
-      if (strcmp (bin_dirs[common], prefix_dirs[common]) != 0)
+      if (FILENAME_CMP (bin_dirs[common], prefix_dirs[common]) != 0)
 	break;
     }
 
diff --git a/libiberty/make-temp-file.c b/libiberty/make-temp-file.c
index cb08c27af6f..d7701e4b38a 100644
--- a/libiberty/make-temp-file.c
+++ b/libiberty/make-temp-file.c
@@ -47,6 +47,7 @@ Boston, MA 02110-1301, USA.  */
 #endif
 
 #include "libiberty.h"
+#include "filenames.h"
 extern int mkstemps (char *, int);
 
 /* '/' works just fine on MS-DOS based systems.  */
@@ -142,7 +143,8 @@ choose_tmpdir (void)
       len = strlen (base);
       tmpdir = XNEWVEC (char, len + 2);
       strcpy (tmpdir, base);
-      tmpdir[len] = DIR_SEPARATOR;
+      if (len>0 && !IS_DIR_SEPARATOR(tmpdir[len-1]))
+          tmpdir[len] = DIR_SEPARATOR;
       tmpdir[len+1] = '\0';
       memoized_tmpdir = tmpdir;
 #else /* defined(_WIN32) && !defined(__CYGWIN__) */
diff --git a/libiberty/simple-object-elf.c b/libiberty/simple-object-elf.c
index 37e73348cb7..0d6f84c1ed3 100644
--- a/libiberty/simple-object-elf.c
+++ b/libiberty/simple-object-elf.c
@@ -1293,7 +1293,9 @@ simple_object_elf_copy_lto_debug_sections (simple_object_read *sobj,
     }
   if (new_i - 1 >= SHN_LORESERVE)
     {
+#ifdef ENOTSUP
       *err = ENOTSUP;
+#endif
       return "Too many copied sections";
     }
   eow->shdrs = XNEWVEC (unsigned char, shdr_size * (new_i - 1));
diff --git a/libquadmath/printf/quadmath-printf.h b/libquadmath/printf/quadmath-printf.h
index 32ebcec928c..96498b7c408 100644
--- a/libquadmath/printf/quadmath-printf.h
+++ b/libquadmath/printf/quadmath-printf.h
@@ -29,7 +29,8 @@ Boston, MA 02110-1301, USA.  */
 #ifdef HAVE_CTYPE_H
 #include <ctype.h>
 #endif
-#ifdef HAVE_WCHAR_H
+#if defined(HAVE_WCHAR_H) && !defined(__DJGPP__)
+/* DJGPP wchar.h is not good enough */
 #include <wchar.h>
 #endif
 #ifdef HAVE_WCTYPE_H
@@ -44,7 +45,7 @@ Boston, MA 02110-1301, USA.  */
 #include "quadmath-imp.h"
 #include "gmp-impl.h"
 
-#ifdef HAVE_WCHAR_H
+#if defined(HAVE_WCHAR_H) && !defined(__DJGPP__)
 #define L_(x) L##x
 #else
 #define L_(x) x
diff --git a/libstdc++-v3/config/os/djgpp/ctype_configure_char.cc b/libstdc++-v3/config/os/djgpp/ctype_configure_char.cc
index 8562c8f52b0..775756ede3f 100644
--- a/libstdc++-v3/config/os/djgpp/ctype_configure_char.cc
+++ b/libstdc++-v3/config/os/djgpp/ctype_configure_char.cc
@@ -45,7 +45,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   ctype<char>::ctype(__c_locale, const mask* __table, bool __del,
 		     size_t __refs)
   : facet(__refs), _M_del(__table != 0 && __del),
-  _M_toupper(__dj_ctype_toupper), _M_tolower(__dj_ctype_tolower),
+  _M_toupper(__dj_ctype_toupper+1), _M_tolower(__dj_ctype_tolower+1),
   _M_table(__table ? __table : classic_table())
   {
     memset(_M_widen, 0, sizeof(_M_widen));
@@ -56,7 +56,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   ctype<char>::ctype(const mask* __table, bool __del, size_t __refs)
   : facet(__refs), _M_del(__table != 0 && __del),
-  _M_toupper(__dj_ctype_toupper), _M_tolower(__dj_ctype_tolower),
+  _M_toupper(__dj_ctype_toupper+1), _M_tolower(__dj_ctype_tolower+1),
   _M_table(__table ? __table : classic_table())
   {
     memset(_M_widen, 0, sizeof(_M_widen));
diff --git a/libstdc++-v3/config/os/djgpp/error_constants.h b/libstdc++-v3/config/os/djgpp/error_constants.h
index 8f947e69e37..d80a5811ca7 100644
--- a/libstdc++-v3/config/os/djgpp/error_constants.h
+++ b/libstdc++-v3/config/os/djgpp/error_constants.h
@@ -33,6 +33,15 @@
 #include <bits/c++config.h>
 #include <cerrno>
 
+#ifndef EOPNOTSUPP
+// Use same value as in wat3222br6.zip file net/watt/sys/djgpp.err
+#define EOPNOTSUPP 52
+#endif
+
+#ifndef ENOTSUP
+#define ENOTSUP 101
+#endif
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -118,9 +127,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 //    not_connected = 				ENOTCONN,
       not_enough_memory = 			ENOMEM,
 
-#ifdef ENOTSUP
       not_supported = 				ENOTSUP,
-#endif
 
 #ifdef ECANCELED
       operation_canceled = 			ECANCELED,
@@ -128,7 +135,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 //    operation_in_progress = 			EINPROGRESS,
       operation_not_permitted = 		EPERM,
-//    operation_not_supported = 		EOPNOTSUPP,
+      operation_not_supported = 		EOPNOTSUPP,
 //    operation_would_block = 			EWOULDBLOCK,
 
 #ifdef EOWNERDEAD
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 69b823a3466..2d005b875e4 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -53,6 +53,11 @@
 # include <algorithm>
 #endif
 
+#if defined(__DJGPP__)
+# define _GLIBCXX_FILESYSTEM_IS_DJGPP 1
+# include <algorithm>
+#endif
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -516,6 +521,8 @@ namespace __detail
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
       return __ch == L'/' || __ch == preferred_separator;
+#elif defined(_GLIBCXX_FILESYSTEM_IS_DJGPP)
+      return __ch == '/' || __ch == '\\';
 #else
       return __ch == '/';
 #endif
@@ -964,6 +971,9 @@ namespace __detail
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
     std::replace(_M_pathname.begin(), _M_pathname.end(), L'/',
 		 preferred_separator);
+#elif defined(_GLIBCXX_FILESYSTEM_IS_DJGPP)
+    std::replace(_M_pathname.begin(), _M_pathname.end(), '\\',
+		 preferred_separator);
 #endif
     return *this;
   }
@@ -1187,7 +1197,7 @@ namespace __detail
   inline bool
   path::is_absolute() const
   {
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+#if defined(_GLIBCXX_FILESYSTEM_IS_WINDOWS) || defined(_GLIBCXX_FILESYSTEM_IS_DJGPP)
     return has_root_name() && has_root_directory();
 #else
     return has_root_directory();
diff --git a/libstdc++-v3/src/c++11/shared_ptr.cc b/libstdc++-v3/src/c++11/shared_ptr.cc
index 162dd6db2f4..2d4108ed64b 100644
--- a/libstdc++-v3/src/c++11/shared_ptr.cc
+++ b/libstdc++-v3/src/c++11/shared_ptr.cc
@@ -35,7 +35,11 @@ namespace __gnu_internal _GLIBCXX_VISIBILITY(hidden)
   get_mutex(unsigned char i)
   {
     // increase alignment to put each lock on a separate cache line
+#ifdef __DJGPP__
+    struct M : __gnu_cxx::__mutex { };
+#else
     struct alignas(64) M : __gnu_cxx::__mutex { };
+#endif
     static M m[mask + 1];
     return m[i];
   }
diff --git a/libstdc++-v3/src/filesystem/path.cc b/libstdc++-v3/src/filesystem/path.cc
index 59eeadc2c0d..158936910bd 100644
--- a/libstdc++-v3/src/filesystem/path.cc
+++ b/libstdc++-v3/src/filesystem/path.cc
@@ -408,8 +408,13 @@ path::_M_split_cmpts()
 	_M_add_root_dir(0);
       ++pos;
     }
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+#if defined(_GLIBCXX_FILESYSTEM_IS_WINDOWS) \
+  || defined(_GLIBCXX_FILESYSTEM_IS_DJGPP)
+#ifdef __DJGPP__
+  else if (len > 1 && _M_pathname[1] == ':')
+#else
   else if (len > 1 && _M_pathname[1] == L':')
+#endif
     {
       // got disk designator
       if (len == 2)