diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -3054,8 +3054,9 @@
         goto onError;
     if (!PyUnicode_Check(unicode)) {
         PyErr_Format(PyExc_TypeError,
-                     "decoder did not return a str object (type=%.400s)",
-                     Py_TYPE(unicode)->tp_name);
+                     "decoder returned '%.400s' instead of 'str', "
+                     "use codecs.encode for bytes->%.400s conversions",
+                     Py_TYPE(unicode)->tp_name, Py_TYPE(unicode)->tp_name);
         Py_DECREF(unicode);
         goto onError;
     }
@@ -3437,8 +3438,9 @@
     }
 
     PyErr_Format(PyExc_TypeError,
-                 "encoder did not return a bytes object (type=%.400s)",
-                 Py_TYPE(v)->tp_name);
+                 "encoder returned '%.400s' instead of 'bytes', "
+                 "use codecs.decode for str->%.400s conversions",
+                 Py_TYPE(v)->tp_name, Py_TYPE(v)->tp_name);
     Py_DECREF(v);
     return NULL;
 }