diff -ru a/Python/errors.c b/Python/errors.c
--- a/Python/errors.c   2015-05-23 18:09:24.000000000 +0200
+++ b/Python/errors.c   2016-03-03 10:24:55.672009294 +0100
@@ -535,7 +535,7 @@
 #endif /* MS_WINDOWS */
 
 void
-_PyErr_BadInternalCall(char *filename, int lineno)
+_PyErr_BadInternalCall(const char *filename, int lineno)
 {
     PyErr_Format(PyExc_SystemError,
                  "%s:%d: bad argument to internal function",
diff -ru a/Include/pyerrors.h b/Include/pyerrors.h
--- a/Include/pyerrors.h	2015-05-23 18:09:00.000000000 +0200
+++ b/Include/pyerrors.h	2016-03-03 11:19:41.762752293 +0100
@@ -215,7 +215,7 @@
 
 /* Export the old function so that the existing API remains available: */
 PyAPI_FUNC(void) PyErr_BadInternalCall(void);
-PyAPI_FUNC(void) _PyErr_BadInternalCall(char *filename, int lineno);
+PyAPI_FUNC(void) _PyErr_BadInternalCall(const char *filename, int lineno);
 /* Mask the old API with a call to the new API for code compiled under
    Python 2.0: */
 #define PyErr_BadInternalCall() _PyErr_BadInternalCall(__FILE__, __LINE__)