diff --git a/Doc/c-api/complex.rst b/Doc/c-api/complex.rst
index 43dfe56..3cff88a 100644
--- a/Doc/c-api/complex.rst
+++ b/Doc/c-api/complex.rst
@@ -63,12 +63,18 @@
    Return the quotient of two complex numbers, using the C :c:type:`Py_complex`
    representation.
 
+   If *divisor* is null, this method returns zero and sets
+   :c:data:`errno` to :c:data:`EDOM`.
+
 
 .. c:function:: Py_complex _Py_c_pow(Py_complex num, Py_complex exp)
 
    Return the exponentiation of *num* by *exp*, using the C :c:type:`Py_complex`
    representation.
 
+   If :attr:`exp.imag` is not null, or :attr:`exp.real` is negative,
+   this method returns zero and sets :c:data:`errno` to :c:data:`EDOM`.
+
 
 Complex Numbers as Python Objects
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -123,4 +129,4 @@
 
    If *op* is not a Python complex number object but has a :meth:`__complex__`
    method, this method will first be called to convert *op* to a Python complex
-   number object.
+   number object. Upon failure, this method returns ``-1.0`` as a real value.
diff --git a/Doc/c-api/float.rst b/Doc/c-api/float.rst
index 757efd3..27a75e3 100644
--- a/Doc/c-api/float.rst
+++ b/Doc/c-api/float.rst
@@ -47,6 +47,8 @@
    Return a C :c:type:`double` representation of the contents of *pyfloat*.  If
    *pyfloat* is not a Python floating point object but has a :meth:`__float__`
    method, this method will first be called to convert *pyfloat* into a float.
+   This method returns ``-1.0`` upon failure, so one should call
+   :c:func:`PyErr_Occurred` to check for errors.
 
 
 .. c:function:: double PyFloat_AS_DOUBLE(PyObject *pyfloat)