diff --git a/NEWS b/NEWS
index 24205b7..cad3d72 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,8 @@ GNU sed NEWS                                    -*- outline -*-
 
 ** Bug fixes
 
+  sed no longer rejects "\c[" in regular expressions
+
   'sed --follow-symlinks -i' no longer mishandles an operand that is a
   short symbolic link to a long symbolic link to a file.
   [bug introduced in sed 4.9]
diff --git a/m4/.gitignore b/m4/.gitignore
index 7124c51..756c4c7 100644
--- a/m4/.gitignore
+++ b/m4/.gitignore
@@ -271,7 +271,6 @@
 /wctype.m4
 /windows-rc.m4
 /xgetcwd.m4
-/getlocalename_l.m4
 /getopt.m4
 /frexp.m4
 /frexpl.m4
diff --git a/sed/compile.c b/sed/compile.c
index 05efd02..86421ea 100644
--- a/sed/compile.c
+++ b/sed/compile.c
@@ -475,8 +475,20 @@ match_slash (int slash, bool regex, bool s_command)
               ch = inchar ();
               if (ch == EOF)
                 break;
-              else if (ch != '\n' && (ch != slash || (!regex && ch == '&')))
+              /* Preserve backslash except when escaping delimiter in regex. */
+              if (ch != '\n' && (ch != slash || (!regex && ch == '&')))
                 add1_buffer (b, '\\');
+              /* Special case: in regex, treat \cX as atomic escape,
+                 but only in GNU-extension mode (not strict POSIX).  */
+              if (regex && ch == 'c' && posixicity != POSIXLY_BASIC) {
+                add1_buffer (b, ch);
+                int next = inchar ();
+                if (next == EOF)
+                  break;
+                add1_buffer (b, next);
+                /* Skip end-of-loop add1_buffer, we already did it.  */
+                continue;
+              }
               if (s_command && posixicity != POSIXLY_EXTENDED && ch != '&'
                   && ch != '\\' && !ISDIGIT (ch) && ch != '\n' && ch != slash)
                 fprintf (stderr, _("%s: warning: using \"\\%c\" in the 's' "
diff --git a/testsuite/misc.pl b/testsuite/misc.pl
index 2ccbd58..0320f36 100644
--- a/testsuite/misc.pl
+++ b/testsuite/misc.pl
@@ -1199,6 +1199,22 @@ s,.*[^\/],,
      ['bug30794_3', "s/z/\\\\x5c1/",  {IN=>'z'}, {OUT => "\\1"}],
 
      ['bug40242', q('sn\nnXn'),  {IN=>'n'}, {OUT => 'X'}],
+
+     # sed 's/\c[//' is valid, but was rejected by sed-4.9 and prior
+     ['bug79519_1', q('s/\c[//'), {IN=>"a\eb"}, {OUT => 'ab'}],
+     # Exercise in a bracket expression.
+     ['bug79519_2', q('s/[\c[a]//g'), {IN=>"a\ebc"}, {OUT => 'bc'}],
+     # With --posix, \c is treated like 'c'
+     ['bug79519_3', qw(--posix), q('s/[\c[a]//g'), {IN=>"a\ebc"}, {OUT => "\eb"}],
+     # Exercise in a search (non-subst) regexp:
+     ['bug79519_4', q('/\c[/d'), {IN=>"a\e\nc\n"}, {OUT => "c\n"}],
+     # sed --posix must reject, since \cX is a GNU-only feature.
+     ['bug79519_fail', qw(--posix), q('s/\c[//'), {IN=>"x"}, {OUT => ''},
+      {ERR => "sed: warning: using \"\\c\" in the 's' command is not portable\n"
+	   . "sed: -e expression #1, char 7: unterminated 's' command\n"
+      },
+      {EXIT => 1},
+     ],
     );
 
 my $save_temps = $ENV{SAVE_TEMPS};