Index: Python/ceval.c
===================================================================
--- Python/ceval.c	(revision 74029)
+++ Python/ceval.c	(working copy)
@@ -3535,7 +3535,7 @@
 		return 1;
 	}
 	Py_DECREF(w);
-	PyErr_SetString(PyExc_ValueError, "too many values to unpack");
+	PyErr_Format(PyExc_ValueError, "too many values to unpack (expected %d)", argcnt);
 	/* fall through */
 Error:
 	for (; i > 0; i--, sp++)