diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 39b7462..bb4036a 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -6001,8 +6001,9 @@
     /* Coerce the two arguments */
     sub = PyUnicode_FromObject(element);
     if (!sub) {
-	PyErr_SetString(PyExc_TypeError,
-	    "'in <string>' requires string as left operand");
+	PyErr_Format(PyExc_TypeError,
+	    "'in <string>' requires string as left operand, not %s",
+	    element->ob_type->tp_name);
         return -1;
     }