Index: Python/ast.c
===================================================================
--- Python/ast.c	(revision 56394)
+++ Python/ast.c	(working copy)
@@ -1319,6 +1319,10 @@
         return Dict(keys, values, LINENO(n), n->n_col_offset, c->c_arena);
     }
     case BACKQUOTE: { /* repr */
+        if (Py_Py3kWarningFlag &&
+            PyErr_Warn(PyExc_DeprecationWarning,
+                "backquote not supported in 3.x") < 0)
+            return NULL;
         expr_ty expression = ast_for_testlist(c, CHILD(n, 1));
         if (!expression)
             return NULL;