Index: subversion/include/svn_opt.h
===================================================================
--- subversion/include/svn_opt.h	(revision 29392)
+++ subversion/include/svn_opt.h	(working copy)
@@ -346,7 +346,10 @@ enum svn_opt_revision_kind {
   svn_opt_revision_working,
 
   /** repository youngest */
-  svn_opt_revision_head
+  svn_opt_revision_head,
+
+  /** repository prior to youngest */
+  svn_opt_revision_prior
 };
 
 /**
Index: subversion/libsvn_subr/opt.c
===================================================================
--- subversion/libsvn_subr/opt.c	(revision 29392)
+++ subversion/libsvn_subr/opt.c	(working copy)
@@ -622,6 +622,19 @@ static char *parse_one_rev(svn_opt_revision_t *rev
       *end = save;
       return end;
     }
+  else if (*str == '-' && apr_isdigit(*(str + 1)))
+    {
+      /* We're dealing with a negative number here. */
+      end = str + 2;
+      while (apr_isdigit(*end))
+        end++;
+      save = *end;
+      *end = '\0';
+      revision->kind = svn_opt_revision_number;
+      revision->value.number = SVN_STR_TO_REV(str);
+      *end = save;
+      return end;
+    }
   else if (apr_isalpha(*str))
     {
       end = str + 1;
@@ -634,6 +647,7 @@ static char *parse_one_rev(svn_opt_revision_t *rev
       *end = save;
       return end;
     }
+
   else
     return NULL;
 }
Index: subversion/libsvn_client/revisions.c
===================================================================
--- subversion/libsvn_client/revisions.c	(revision 29392)
+++ subversion/libsvn_client/revisions.c	(working copy)
@@ -49,6 +49,7 @@ svn_client__get_revision_number(svn_revnum_t *revn
       *revnum = revision->value.number;
       break;
 
+    case svn_opt_revision_prior:
     case svn_opt_revision_head:
       /* If our caller provided a value for HEAD that he wants us to
          use, we'll use it.  Otherwise, we have to query the
@@ -67,6 +68,11 @@ svn_client__get_revision_number(svn_revnum_t *revn
           if (youngest_rev)
             *youngest_rev = *revnum;
         }
+
+      /* We want HEAD - 1 when 'prior' */
+      if (revision->kind == svn_opt_revision_prior)
+        --(*revnum);
+
       break;
 
     case svn_opt_revision_committed:
Index: subversion/tests/cmdline/diff_tests.py
===================================================================
--- subversion/tests/cmdline/diff_tests.py	(revision 29392)
+++ subversion/tests/cmdline/diff_tests.py	(working copy)
@@ -3343,6 +3343,27 @@ def diff_file_depth_empty(sbox):
   if len(out) < 4:
     raise svntest.Failure
 
+def diff_change_head_keyword(sbox):
+  "diff using -cHEAD"
+
+  sbox.build()
+  os.chdir(sbox.wc_dir)
+
+  add_a_file_in_a_subdir()
+  update_a_file()
+
+  svntest.main.run_svn(None, 'ci', '-m', 'log msg')
+
+  diff_output, err_output = svntest.main.run_svn(None, 'diff',
+                                                 '-c', 'HEAD')
+
+  diff_output2, err_output2 = svntest.main.run_svn(None, 'diff',
+                                                   '-r', '1:2')
+
+  if diff_output != diff_output2:
+    raise svntest.Failure
+
+
 ########################################################################
 #Run the tests
 
@@ -3396,6 +3417,7 @@ test_list = [ None,
               diff_backward_repos_wc_copy,
               diff_summarize_xml,
               diff_file_depth_empty,
+              diff_change_head_keyword,
               ]
 
 if __name__ == '__main__':
Index: subversion/svn/main.c
===================================================================
--- subversion/svn/main.c	(revision 29392)
+++ subversion/svn/main.c	(working copy)
@@ -1193,9 +1193,8 @@ main(int argc, const char *argv[])
         break;
       case 'c':
         {
-          char *end;
-          svn_revnum_t changeno;
-          svn_opt_revision_range_t *range;
+          svn_opt_revision_range_t *range = apr_palloc(pool,
+                                                       sizeof(*range));
 
           if (opt_state.old_target)
             {
@@ -1204,41 +1203,73 @@ main(int argc, const char *argv[])
                  _("Can't specify -c with --old"));
               return svn_cmdline_handle_exit_error(err, pool, "svn: ");
             }
-          changeno = strtol(opt_arg, &end, 10);
-          if (end == opt_arg || *end != '\0')
+
+          /* The first move is to use svn_opt_parse_revision() to
+           * extract the revision argument into the range structure. */
+          if (svn_opt_parse_revision(&range->start, &range->end,
+                                     opt_arg, pool) != 0)
             {
-              err = svn_error_create(SVN_ERR_CL_ARG_PARSING_ERROR, NULL,
-                                     _("Non-numeric change argument "
-                                       "given to -c"));
+              err = svn_utf_cstring_to_utf8(&utf8_opt_arg, opt_arg, pool);
+              if (! err)
+                err = svn_error_createf
+                  (SVN_ERR_CL_ARG_PARSING_ERROR, NULL,
+                   _("Syntax error in revision argument '%s'"),
+                   utf8_opt_arg);
               return svn_cmdline_handle_exit_error(err, pool, "svn: ");
             }
-          if (changeno == 0)
+
+          /* Sanity check: only range->start should be set with -c. */
+          if (range->end.kind != svn_opt_revision_unspecified)
             {
-              err = svn_error_create(SVN_ERR_CL_ARG_PARSING_ERROR, NULL,
-                                     _("There is no change 0"));
+              err = svn_error_create
+                (SVN_ERR_CL_ARG_PARSING_ERROR, NULL,
+                 _("Multiple revision arguments encountered; "
+                   "can't specify N:M range with -c, "
+                   "try '-r N:M' instead"));
               return svn_cmdline_handle_exit_error(err, pool, "svn: ");
             }
 
-          /* Figure out the range:
-                -c N  -> -r N-1:N
-                -c -N -> -r N:N-1 */
-          range = apr_palloc(pool, sizeof(*range));
-          if (changeno > 0)
+          /* Then we check for the type, is it a number or HEAD? */
+          if (range->start.kind == svn_opt_revision_number)
             {
-              range->start.value.number = changeno - 1;
-              range->end.value.number = changeno;
+              svn_revnum_t change_rev = range->start.value.number;
+
+              /* Figure out the range:
+                    -c 0  -> invalid
+                    -c N  -> -r N-1:N
+                    -c -N -> -r N:N-1 */
+              if (change_rev == 0)
+                {
+                  err = svn_error_create(SVN_ERR_CL_ARG_PARSING_ERROR, NULL,
+                                         _("There is no change 0"));
+                  return svn_cmdline_handle_exit_error(err, pool, "svn: ");
+                }
+              else if (change_rev > 0)
+                {
+                  range->start.value.number = change_rev - 1;
+                  range->end.value.number = change_rev;
+                }
+              else
+                {
+                  change_rev = -change_rev;
+                  range->start.value.number = change_rev;
+                  range->end.value.number = change_rev - 1;
+                }
+
+              range->end.kind = svn_opt_revision_number;
             }
-          else
+          else if (range->start.kind == svn_opt_revision_head)
             {
-              changeno = -changeno;
-              range->start.value.number = changeno;
-              range->end.value.number = changeno - 1;
+              range->start.kind = svn_opt_revision_prior;
+              range->end.kind = svn_opt_revision_head;
+              range->start.value.number = SVN_IGNORED_REVNUM;
+              range->end.value.number = SVN_IGNORED_REVNUM;
             }
-          opt_state.used_change_arg = TRUE;
-          range->start.kind = svn_opt_revision_number;
-          range->end.kind = svn_opt_revision_number;
+
           APR_ARRAY_PUSH(opt_state.revision_ranges,
                          svn_opt_revision_range_t *) = range;
+
+          opt_state.used_change_arg = TRUE;
         }
         break;
       case 'r':