diff -r 0e07ab605e0b Doc/library/json.rst
--- a/Doc/library/json.rst	Sun Dec 15 20:56:00 2013 -0500
+++ b/Doc/library/json.rst	Mon Dec 16 18:43:23 2013 +0800
@@ -226,7 +226,10 @@
    *parse_float*, if specified, will be called with the string of every JSON
    float to be decoded.  By default, this is equivalent to ``float(num_str)``.
    This can be used to use another datatype or parser for JSON floats
-   (e.g. :class:`decimal.Decimal`).
+   (e.g. :class:`decimal.Decimal`). Note that this does not mean we can pass
+   non-valid JSON number string but valid Python number string, such as '.5'
+   to JSON parser because *parse_float* will be only triggered after the number
+   string is tokenized.
 
    *parse_int*, if specified, will be called with the string of every JSON int
    to be decoded.  By default, this is equivalent to ``int(num_str)``.  This can
@@ -312,7 +315,10 @@
    *parse_float*, if specified, will be called with the string of every JSON
    float to be decoded.  By default, this is equivalent to ``float(num_str)``.
    This can be used to use another datatype or parser for JSON floats
-   (e.g. :class:`decimal.Decimal`).
+   (e.g. :class:`decimal.Decimal`). Note that this does not mean we can pass
+   non-valid JSON number string but valid Python number string, such as '.5'
+   to JSON parser because *parse_float* will be only triggered after the number
+   string is tokenized.
 
    *parse_int*, if specified, will be called with the string of every JSON int
    to be decoded.  By default, this is equivalent to ``int(num_str)``.  This can
diff -r 0e07ab605e0b Lib/test/test_json/test_fail.py
--- a/Lib/test/test_json/test_fail.py	Sun Dec 15 20:56:00 2013 -0500
+++ b/Lib/test/test_json/test_fail.py	Mon Dec 16 18:43:23 2013 +0800
@@ -71,6 +71,8 @@
     '["mismatch"}',
     # http://code.google.com/p/simplejson/issues/detail?id=3
     '["A\u001FZ control characters in string"]',
+    # Valid Python number string but invalid JSON number string
+    '[.5]',
 ]
 
 SKIPS = {