Index: subversion/libsvn_wc/update_editor.c
===================================================================
--- subversion/libsvn_wc/update_editor.c	(revision 20900)
+++ subversion/libsvn_wc/update_editor.c	(working copy)
@@ -1498,6 +1498,14 @@
                                "is not a versioned resource"),
                              fb->name,
                              svn_path_local_style(pb->path, pool));
+
+  /* Make sure the file is not exclusively opened by someone else. */
+  if (!adding && entry && entry->schedule != svn_wc_schedule_delete)
+  {
+    apr_file_t* file;
+    SVN_ERR(svn_io_file_open(&file, fb->path, APR_READ, APR_OS_DEFAULT,
+                             subpool));
+  }
   
   /* ### todo:  right now the incoming copyfrom* args are being
      completely ignored!  Someday the editor-driver may expect us to