diff -r 14cf0011c5e9 Include/pyerrors.h
--- a/Include/pyerrors.h	Fri Apr 15 10:51:46 2016 -0700
+++ b/Include/pyerrors.h	Sat Apr 16 11:02:17 2016 +0300
@@ -293,6 +293,17 @@ PyAPI_FUNC(void) _PyErr_BadInternalCall(
    Python 2.0: */
 #define PyErr_BadInternalCall() _PyErr_BadInternalCall(__FILE__, __LINE__)
 
+#ifdef Py_DEBUG
+#define _Py_CHECK_NO_ERRORS(ret)  do {  \
+        if (PyErr_Occurred()) {         \
+            PyErr_BadInternalCall();    \
+            return (ret);               \
+        }                               \
+    } while (0);
+#else
+#define _Py_CHECK_NO_ERRORS(ret)  assert(!PyErr_Occurred())
+#endif
+
 /* Function to create a new exception */
 PyAPI_FUNC(PyObject *) PyErr_NewException(
     const char *name, PyObject *base, PyObject *dict);
diff -r 14cf0011c5e9 Objects/abstract.c
--- a/Objects/abstract.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Objects/abstract.c	Sat Apr 16 11:02:17 2016 +0300
@@ -2780,6 +2780,7 @@ PyObject *
 PyIter_Next(PyObject *iter)
 {
     PyObject *result;
+    _Py_CHECK_NO_ERRORS(NULL);
     result = (*iter->ob_type->tp_iternext)(iter);
     if (result == NULL &&
         PyErr_Occurred() &&
diff -r 14cf0011c5e9 Objects/complexobject.c
--- a/Objects/complexobject.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Objects/complexobject.c	Sat Apr 16 11:02:17 2016 +0300
@@ -292,17 +292,18 @@ PyComplex_AsCComplex(PyObject *op)
     Py_complex cv;
     PyObject *newop = NULL;
 
+    /* return -1 on failure */
+    cv.real = -1.;
+    cv.imag = 0.;
+
     assert(op);
+    _Py_CHECK_NO_ERRORS(cv);
     /* If op is already of type PyComplex_Type, return its value */
     if (PyComplex_Check(op)) {
         return ((PyComplexObject *)op)->cval;
     }
     /* If not, use op's __complex__  method, if it exists */
 
-    /* return -1 on failure */
-    cv.real = -1.;
-    cv.imag = 0.;
-
     newop = try_complex_special_method(op);
 
     if (newop) {
diff -r 14cf0011c5e9 Objects/floatobject.c
--- a/Objects/floatobject.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Objects/floatobject.c	Sat Apr 16 11:02:17 2016 +0300
@@ -218,13 +218,14 @@ PyFloat_AsDouble(PyObject *op)
     PyFloatObject *fo;
     double val;
 
-    if (op && PyFloat_Check(op))
-        return PyFloat_AS_DOUBLE((PyFloatObject*) op);
-
     if (op == NULL) {
         PyErr_BadArgument();
         return -1;
     }
+    _Py_CHECK_NO_ERRORS(-1.0);
+
+    if (PyFloat_Check(op))
+        return PyFloat_AS_DOUBLE((PyFloatObject*) op);
 
     if ((nb = Py_TYPE(op)->tp_as_number) == NULL || nb->nb_float == NULL) {
         PyErr_SetString(PyExc_TypeError, "a float is required");
@@ -2279,6 +2280,7 @@ double
 double
 _PyFloat_Unpack8(const unsigned char *p, int le)
 {
+    _Py_CHECK_NO_ERRORS(-1.0);
     if (double_format == unknown_format) {
         unsigned char sign;
         int e;
diff -r 14cf0011c5e9 Objects/longobject.c
--- a/Objects/longobject.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Objects/longobject.c	Sat Apr 16 11:02:17 2016 +0300
@@ -403,6 +403,7 @@ PyLong_AsLongAndOverflow(PyObject *vv, i
         PyErr_BadInternalCall();
         return -1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
 
     if (PyLong_Check(vv)) {
         v = (PyLongObject *)vv;
@@ -512,6 +513,7 @@ PyLong_AsSsize_t(PyObject *vv) {
         PyErr_BadInternalCall();
         return -1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
     if (!PyLong_Check(vv)) {
         PyErr_SetString(PyExc_TypeError, "an integer is required");
         return -1;
@@ -567,6 +569,7 @@ PyLong_AsUnsignedLong(PyObject *vv)
         PyErr_BadInternalCall();
         return (unsigned long)-1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
     if (!PyLong_Check(vv)) {
         PyErr_SetString(PyExc_TypeError, "an integer is required");
         return (unsigned long)-1;
@@ -611,6 +614,7 @@ PyLong_AsSize_t(PyObject *vv)
         PyErr_BadInternalCall();
         return (size_t) -1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
     if (!PyLong_Check(vv)) {
         PyErr_SetString(PyExc_TypeError, "an integer is required");
         return (size_t)-1;
@@ -683,6 +687,7 @@ PyLong_AsUnsignedLongMask(PyObject *op)
         PyErr_BadInternalCall();
         return (unsigned long)-1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
 
     if (PyLong_Check(op)) {
         return _PyLong_AsUnsignedLongMask(op);
@@ -1202,6 +1207,7 @@ PyLong_AsLongLong(PyObject *vv)
         PyErr_BadInternalCall();
         return -1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
 
     if (PyLong_Check(vv)) {
         v = (PyLongObject *)vv;
@@ -1253,6 +1259,7 @@ PyLong_AsUnsignedLongLong(PyObject *vv)
         PyErr_BadInternalCall();
         return (unsigned PY_LONG_LONG)-1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
     if (!PyLong_Check(vv)) {
         PyErr_SetString(PyExc_TypeError, "an integer is required");
         return (unsigned PY_LONG_LONG)-1;
@@ -1317,6 +1324,7 @@ PyLong_AsUnsignedLongLongMask(PyObject *
         PyErr_BadInternalCall();
         return (unsigned long)-1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
 
     if (PyLong_Check(op)) {
         return _PyLong_AsUnsignedLongLongMask(op);
@@ -1357,6 +1365,7 @@ PyLong_AsLongLongAndOverflow(PyObject *v
         PyErr_BadInternalCall();
         return -1;
     }
+    _Py_CHECK_NO_ERRORS(-1);
 
     if (PyLong_Check(vv)) {
         v = (PyLongObject *)vv;
@@ -2654,6 +2663,7 @@ double
        multiple of 4, rounding ties to a multiple of 8. */
     static const int half_even_correction[8] = {0, -1, -2, 1, 0, -1, 2, 1};
 
+    _Py_CHECK_NO_ERRORS(-1.0);
     a_size = Py_ABS(Py_SIZE(a));
     if (a_size == 0) {
         /* Special case for 0: significand 0.0, exponent 0. */
@@ -2765,6 +2775,7 @@ PyLong_AsDouble(PyObject *v)
         PyErr_BadInternalCall();
         return -1.0;
     }
+    _Py_CHECK_NO_ERRORS(-1.0);
     if (!PyLong_Check(v)) {
         PyErr_SetString(PyExc_TypeError, "an integer is required");
         return -1.0;
diff -r 14cf0011c5e9 Objects/typeobject.c
--- a/Objects/typeobject.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Objects/typeobject.c	Sat Apr 16 11:02:17 2016 +0300
@@ -2852,6 +2852,7 @@ PyObject *
     PyObject *mro, *res, *base, *dict;
     unsigned int h;
 
+    _Py_CHECK_NO_ERRORS(NULL);
     if (MCACHE_CACHEABLE_NAME(name) &&
         PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
         /* fast path */
diff -r 14cf0011c5e9 Python/errors.c
--- a/Python/errors.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Python/errors.c	Sat Apr 16 11:02:17 2016 +0300
@@ -746,9 +746,12 @@ PyErr_SetImportError(PyObject *msg, PyOb
 void
 _PyErr_BadInternalCall(const char *filename, int lineno)
 {
+    PyObject *exc, *val, *tb;
+    PyErr_Fetch(&exc, &val, &tb);
     PyErr_Format(PyExc_SystemError,
                  "%s:%d: bad argument to internal function",
                  filename, lineno);
+    _PyErr_ChainExceptions(exc, val, tb);
 }
 
 /* Remove the preprocessor macro for PyErr_BadInternalCall() so that we can
diff -r 14cf0011c5e9 Python/marshal.c
--- a/Python/marshal.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Python/marshal.c	Sat Apr 16 11:02:17 2016 +0300
@@ -747,6 +747,7 @@ r_short(RFILE *p)
     short x = -1;
     const unsigned char *buffer;
 
+    _Py_CHECK_NO_ERRORS(-1);
     buffer = (const unsigned char *) r_string(2, p);
     if (buffer != NULL) {
         x = buffer[0];
@@ -763,6 +764,7 @@ r_long(RFILE *p)
     long x = -1;
     const unsigned char *buffer;
 
+    _Py_CHECK_NO_ERRORS(-1);
     buffer = (const unsigned char *) r_string(4, p);
     if (buffer != NULL) {
         x = buffer[0];
diff -r 14cf0011c5e9 Python/pystrtod.c
--- a/Python/pystrtod.c	Fri Apr 15 10:51:46 2016 -0700
+++ b/Python/pystrtod.c	Sat Apr 16 11:02:17 2016 +0300
@@ -341,6 +341,7 @@ PyOS_string_to_double(const char *s,
     double x, result=-1.0;
     char *fail_pos;
 
+    _Py_CHECK_NO_ERRORS(-1.0);
     errno = 0;
     PyFPE_START_PROTECT("PyOS_string_to_double", return -1.0)
     x = _PyOS_ascii_strtod(s, &fail_pos);