Index: conflicts.c
===================================================================
--- conflicts.c	(revision 1727868)
+++ conflicts.c	(working copy)
@@ -1628,6 +1628,14 @@
       case svn_wc_conflict_choose_theirs_conflict:
       case svn_wc_conflict_choose_mine_conflict:
         {
+          if (mine_abspath == NULL)
+            return svn_error_createf(SVN_ERR_WC_CONFLICT_RESOLVER_FAILURE, NULL,
+                                     _("Conflict on '%s' could not be "
+                                       "resolved because the chosen version of "
+                                       "the file is not available."),
+                                     svn_dirent_local_style(local_abspath,
+                                                            scratch_pool));
+
           svn_diff_conflict_display_style_t style
             = choice == svn_wc_conflict_choose_theirs_conflict
                 ? svn_diff_conflict_display_latest