diff -r d5d0b62c2830 Lib/test/test_capi.py
--- a/Lib/test/test_capi.py	Thu Jan 28 21:43:51 2016 +0200
+++ b/Lib/test/test_capi.py	Fri Jan 29 01:06:47 2016 +0200
@@ -488,10 +488,10 @@ class SkipitemTest(unittest.TestCase):
                 _testcapi.parse_tuple_and_keywords(tuple_1, dict_b,
                     format.encode("ascii"), keywords)
                 when_not_skipped = False
-            except TypeError as e:
-                s = "argument 1 must be impossible<bad format char>, not int"
+            except SystemError as e:
+                s = "argument 1 (impossible<bad format char>)"
                 when_not_skipped = (str(e) == s)
-            except RuntimeError as e:
+            except (TypeError, RuntimeError):
                 when_not_skipped = False
 
             # test the format unit when skipped
diff -r d5d0b62c2830 Lib/test/test_getargs2.py
--- a/Lib/test/test_getargs2.py	Thu Jan 28 21:43:51 2016 +0200
+++ b/Lib/test/test_getargs2.py	Fri Jan 29 01:06:47 2016 +0200
@@ -636,10 +636,10 @@ class String_TestCase(unittest.TestCase)
         self.assertEqual(getargs_es_hash('abc\xe9', 'latin1', buf), b'abc\xe9')
         self.assertEqual(buf, bytearray(b'abc\xe9\x00'))
         buf = bytearray(b'x'*4)
-        self.assertRaises(TypeError, getargs_es_hash, 'abc\xe9', 'latin1', buf)
+        self.assertRaises(ValueError, getargs_es_hash, 'abc\xe9', 'latin1', buf)
         self.assertEqual(buf, bytearray(b'x'*4))
         buf = bytearray()
-        self.assertRaises(TypeError, getargs_es_hash, 'abc\xe9', 'latin1', buf)
+        self.assertRaises(ValueError, getargs_es_hash, 'abc\xe9', 'latin1', buf)
 
     def test_et_hash(self):
         from _testcapi import getargs_et_hash
@@ -662,10 +662,10 @@ class String_TestCase(unittest.TestCase)
         self.assertEqual(getargs_et_hash('abc\xe9', 'latin1', buf), b'abc\xe9')
         self.assertEqual(buf, bytearray(b'abc\xe9\x00'))
         buf = bytearray(b'x'*4)
-        self.assertRaises(TypeError, getargs_et_hash, 'abc\xe9', 'latin1', buf)
+        self.assertRaises(ValueError, getargs_et_hash, 'abc\xe9', 'latin1', buf)
         self.assertEqual(buf, bytearray(b'x'*4))
         buf = bytearray()
-        self.assertRaises(TypeError, getargs_et_hash, 'abc\xe9', 'latin1', buf)
+        self.assertRaises(ValueError, getargs_et_hash, 'abc\xe9', 'latin1', buf)
 
     def test_u(self):
         from _testcapi import getargs_u
diff -r d5d0b62c2830 Python/getargs.c
--- a/Python/getargs.c	Thu Jan 28 21:43:51 2016 +0200
+++ b/Python/getargs.c	Fri Jan 29 01:06:47 2016 +0200
@@ -342,7 +342,7 @@ vgetargs1(PyObject *args, const char *fo
                           flags, levels, msgbuf,
                           sizeof(msgbuf), &freelist);
         if (msg) {
-            seterror(i+1, msg, levels, fname, msg);
+            seterror(i+1, msg, levels, fname, message);
             return cleanreturn(0, &freelist);
         }
     }
@@ -394,7 +394,12 @@ seterror(Py_ssize_t iarg, const char *ms
         PyOS_snprintf(p, sizeof(buf) - (p - buf), " %.256s", msg);
         message = buf;
     }
-    PyErr_SetString(PyExc_TypeError, message);
+    if (msg[0] == '(') {
+        PyErr_SetString(PyExc_SystemError, message);
+    }
+    else {
+        PyErr_SetString(PyExc_TypeError, message);
+    }
 }
 
 
@@ -535,9 +540,15 @@ converterr(const char *expected, PyObjec
 {
     assert(expected != NULL);
     assert(arg != NULL);
-    PyOS_snprintf(msgbuf, bufsize,
-                  "must be %.50s, not %.50s", expected,
-                  arg == Py_None ? "None" : arg->ob_type->tp_name);
+    if (expected[0] == '(') {
+        PyOS_snprintf(msgbuf, bufsize,
+                      "%.100s", expected);
+    }
+    else {
+        PyOS_snprintf(msgbuf, bufsize,
+                      "must be %.50s, not %.50s", expected,
+                      arg == Py_None ? "None" : arg->ob_type->tp_name);
+    }
     return msgbuf;
 }
 
@@ -741,7 +752,7 @@ convertsimple(PyObject *arg, const char 
         if (PyLong_Check(arg))
             ival = PyLong_AsUnsignedLongMask(arg);
         else
-            return converterr("integer<k>", arg, msgbuf, bufsize);
+            return converterr("int", arg, msgbuf, bufsize);
         *p = ival;
         break;
     }
@@ -766,7 +777,7 @@ convertsimple(PyObject *arg, const char 
         if (PyLong_Check(arg))
             ival = PyLong_AsUnsignedLongLongMask(arg);
         else
-            return converterr("integer<K>", arg, msgbuf, bufsize);
+            return converterr("int", arg, msgbuf, bufsize);
         *p = ival;
         break;
     }
@@ -1123,9 +1134,11 @@ convertsimple(PyObject *arg, const char 
             } else {
                 if (size + 1 > BUFFER_LEN) {
                     Py_DECREF(s);
-                    return converterr(
-                        "(buffer overflow)",
-                        arg, msgbuf, bufsize);
+                    PyErr_Format(PyExc_ValueError,
+                                 "encoded string too long "
+                                 "(%zd, maximum length %zd)",
+                                 size, (Py_ssize_t)(BUFFER_LEN-1));
+                    RETURN_ERR_OCCURRED;
                 }
             }
             memcpy(*buffer, ptr, size+1);
@@ -1147,7 +1160,7 @@ convertsimple(PyObject *arg, const char 
             if ((Py_ssize_t)strlen(ptr) != size) {
                 Py_DECREF(s);
                 return converterr(
-                    "encoded string without NULL bytes",
+                    "encoded string without null bytes",
                     arg, msgbuf, bufsize);
             }
             *buffer = PyMem_NEW(char, size + 1);
@@ -1237,7 +1250,7 @@ convertsimple(PyObject *arg, const char 
 
         if (*format != '*')
             return converterr(
-                "invalid use of 'w' format character",
+                "(invalid use of 'w' format character)",
                 arg, msgbuf, bufsize);
         format++;
 
@@ -1261,7 +1274,7 @@ convertsimple(PyObject *arg, const char 
     }
 
     default:
-        return converterr("impossible<bad format char>", arg, msgbuf, bufsize);
+        return converterr("(impossible<bad format char>)", arg, msgbuf, bufsize);
 
     }