Index: subversion/libsvn_client/checkout.c
===================================================================
--- subversion/libsvn_client/checkout.c	(revision 18289)
+++ subversion/libsvn_client/checkout.c	(working copy)
@@ -65,7 +65,7 @@
   assert (url != NULL);
 
   /* Fulfill the docstring promise of svn_client_checkout: */
-  if ((revision->kind != svn_opt_revision_number)
+  if (revision && (revision->kind != svn_opt_revision_number)
       && (revision->kind != svn_opt_revision_date)
       && (revision->kind != svn_opt_revision_head))
     return svn_error_create (SVN_ERR_CLIENT_BAD_REVISION, NULL, NULL);