diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 1e71198..756d722 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -434,7 +434,8 @@
 
    Convert a string or a number to floating point.  If the argument is a string, it
    must contain a possibly signed decimal or floating point number, possibly
-   embedded in whitespace. Otherwise, the argument may be a plain or long integer
+   embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf.
+   Otherwise, the argument may be a plain or long integer
    or a floating point number, and a floating point number with the same value
    (within Python's floating point precision) is returned.  If no argument is
    given, returns ``0.0``.
@@ -446,9 +447,10 @@
          single: Infinity
 
       When passing in a string, values for NaN and Infinity may be returned, depending
-      on the underlying C library.  The specific set of strings accepted which cause
-      these values to be returned depends entirely on the C library and is known to
-      vary.
+      on the underlying C library.  Float accepts the strings nan, inf and -inf for
+      NaN and positive or negative infinity. The case and a leading + are ignored as
+      well as a leading - is ignored for NaN. Float always represents NaN and infinity
+      as nan, inf or -inf.
 
    The float type is described in :ref:`typesnumeric`.
 
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index f7363c3..5b341b8 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -298,7 +298,7 @@
 +--------------------+---------------------------------+--------+
 | ``long(x)``        | *x* converted to long integer   | \(2)   |
 +--------------------+---------------------------------+--------+
-| ``float(x)``       | *x* converted to floating point |        |
+| ``float(x)``       | *x* converted to floating point | \(6)   |
 +--------------------+---------------------------------+--------+
 | ``complex(re,im)`` | a complex number with real part |        |
 |                    | *re*, imaginary part *im*.      |        |
@@ -355,6 +355,13 @@
    Also referred to as integer division.  The resultant value is a whole integer,
    though the result's type is not necessarily int.
 
+(6)
+   float also accepts the strings "nan" and "inf" with an optional prefix "+" 
+   or "-" for Not a Number (NaN) and positive or negative infinity.
+   
+   .. versionadded:: 2.6
+
+   
 .. % XXXJH exceptions: overflow (when? what operations?) zerodivision