diff --git a/Doc/library/cmath.rst b/Doc/library/cmath.rst
index 14b909b..ae94039 100644
--- a/Doc/library/cmath.rst
+++ b/Doc/library/cmath.rst
@@ -187,6 +187,12 @@
 Classification functions
 ------------------------
 
+.. function:: isfinite(x)
+
+   Return ``True`` if both the real and imaginary parts of *x* are finite,
+   and ``False`` otherwise.
+
+
 .. function:: isinf(x)
 
    Return *True* if the real or the imaginary part of x is positive
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index 9c3bd03..22f6f5f 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -97,6 +97,12 @@
    <http://code.activestate.com/recipes/393090/>`_\.
 
 
+.. function:: isfinite(x)
+
+   Return ``True`` if *x* is neither an infinity nor a NaN, and
+   ``False`` otherwise.  (Note that ``0.0`` *is* considered finite.)
+
+
 .. function:: isinf(x)
 
    Check if the float *x* is positive or negative infinity.