diff --git a/Misc/NEWS b/Misc/NEWS
index 83f1c9614905..ae40187951db 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -17,6 +17,12 @@ Core and Builtins
 Library
 -------
 
+Extension Modules
+-----------------
+
+- Issue #3643: Added a few more checks to _testcapi to prevent segfaults by
+  exploitation of poor argument checking.
+
 
 What's new in Python 3.0b3?
 ===========================
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 494937aa4e17..995d789cfa6d 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -961,6 +961,10 @@ exception_print(PyObject *self, PyObject *args)
 	if (!PyArg_ParseTuple(args, "O:exception_print",
 				&value))
 		return NULL;
+	if (!PyExceptionInstance_Check(value)) {
+		PyErr_Format(PyExc_TypeError, "an exception instance is required");
+		return NULL;
+	}
 
 	tb = PyException_GetTraceback(value);
 	PyErr_Display((PyObject *) Py_TYPE(value), value, tb);