diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 1eb0c2b..38d214a 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -685,7 +685,10 @@
 	return NULL;
 }
 
-PyDoc_STRVAR(math_factorial_doc, "Return n!");
+PyDoc_STRVAR(math_factorial_doc,
+"factorial(x) -> Integral\n"
+"\n"
+"Find x!. Raise a ValueError if x is negative or non-integral.");
 
 static PyObject *
 math_trunc(PyObject *self, PyObject *number)
@@ -837,7 +840,7 @@
 "modf(x)\n"
 "\n"
 "Return the fractional and integer parts of x.  Both results carry the sign\n"
-"of x.  The integer part is returned as a real.");
+"of x and are floats.");
 
 /* A decent logarithm is easy to compute even for huge longs, but libm can't
    do that by itself -- loghelper can.  func is log or log10, and name is