diff --git a/IPython/nbformat/current.py b/IPython/nbformat/current.py
index 2396d14..d2e4562 100644
--- a/IPython/nbformat/current.py
+++ b/IPython/nbformat/current.py
@@ -28,7 +28,8 @@ from IPython.nbformat import v1
 from IPython.nbformat.v3 import (
     NotebookNode,
     new_code_cell, new_text_cell, new_notebook, new_output, new_worksheet,
-    parse_filename, new_metadata, new_author, new_heading_cell, nbformat
+    parse_filename, new_metadata, new_author, new_heading_cell, nbformat,
+    nbformat_minor,
 )
 
 #-----------------------------------------------------------------------------
@@ -36,6 +37,8 @@ from IPython.nbformat.v3 import (
 #-----------------------------------------------------------------------------
 
 current_nbformat = nbformat
+current_nbformat_minor = nbformat_minor
+
 
 
 class NBFormatError(Exception):
@@ -45,8 +48,9 @@ class NBFormatError(Exception):
 def parse_json(s, **kwargs):
     """Parse a string into a (nbformat, dict) tuple."""
     d = json.loads(s, **kwargs)
-    nbf = d.get('nbformat',1)
-    return nbf, d
+    nbf = d.get('nbformat', 1)
+    nbm = d.get('nbformat_minor', 0)
+    return nbf, nbm, d
 
 
 def parse_py(s, **kwargs):
@@ -62,9 +66,7 @@ def parse_py(s, **kwargs):
 
 def reads_json(s, **kwargs):
     """Read a JSON notebook from a string and return the NotebookNode object."""
-    nbf, d = parse_json(s, **kwargs)
-    # cast int for reading - 3.x notebooks should be readable on 3.0, etc.
-    nbf = int(nbf)
+    nbf, minor, d = parse_json(s, **kwargs)
     if nbf == 1:
         nb = v1.to_notebook_json(d, **kwargs)
         nb = v3.convert_to_this_nbformat(nb, orig_version=1)
@@ -73,6 +75,7 @@ def reads_json(s, **kwargs):
         nb = v3.convert_to_this_nbformat(nb, orig_version=2)
     elif nbf == 3:
         nb = v3.to_notebook_json(d, **kwargs)
+        nb = v3.convert_to_this_nbformat(nb, orig_version=3, orig_minor=minor)
     else:
         raise NBFormatError('Unsupported JSON nbformat version: %i' % nbf)
     return nb
@@ -85,8 +88,7 @@ def writes_json(nb, **kwargs):
 def reads_py(s, **kwargs):
     """Read a .py notebook from a string and return the NotebookNode object."""
     nbf, s = parse_py(s, **kwargs)
-    # cast int for reading - 3.x notebooks should be readable on 3.0, etc.
-    nbf = int(nbf)
+    nbf = nbf
     if nbf == 2:
         nb = v2.to_notebook_py(s, **kwargs)
     elif nbf == 3:
diff --git a/IPython/nbformat/v3/__init__.py b/IPython/nbformat/v3/__init__.py
index c8fa25d..d3838e3 100644
--- a/IPython/nbformat/v3/__init__.py
+++ b/IPython/nbformat/v3/__init__.py
@@ -19,7 +19,7 @@ Authors:
 from .nbbase import (
     NotebookNode,
     new_code_cell, new_text_cell, new_notebook, new_output, new_worksheet,
-    new_metadata, new_author, new_heading_cell, nbformat
+    new_metadata, new_author, new_heading_cell, nbformat, nbformat_minor
 )
 
 from .nbjson import reads as reads_json, writes as writes_json
diff --git a/IPython/nbformat/v3/convert.py b/IPython/nbformat/v3/convert.py
index 8914fef..6421b80 100644
--- a/IPython/nbformat/v3/convert.py
+++ b/IPython/nbformat/v3/convert.py
@@ -17,7 +17,8 @@ Authors:
 #-----------------------------------------------------------------------------
 
 from .nbbase import (
-    new_code_cell, new_text_cell, new_worksheet, new_notebook, new_output
+    new_code_cell, new_text_cell, new_worksheet, new_notebook, new_output,
+    nbformat, nbformat_minor
 )
 
 from IPython.nbformat import v2
@@ -26,7 +27,7 @@ from IPython.nbformat import v2
 # Code
 #-----------------------------------------------------------------------------
 
-def convert_to_this_nbformat(nb, orig_version=2):
+def convert_to_this_nbformat(nb, orig_version=2, orig_minor=0):
     """Convert a notebook to the v3 format.
 
     Parameters
@@ -35,16 +36,23 @@ def convert_to_this_nbformat(nb, orig_version=2):
         The Python representation of the notebook to convert.
     orig_version : int
         The original version of the notebook to convert.
+    orig_minor : int
+        The original minor version of the notebook to convert (only relevant for v >= 3).
     """
     if orig_version == 1:
         nb = v2.convert_to_this_nbformat(nb)
         orig_version = 2
     if orig_version == 2:
         # Mark the original nbformat so consumers know it has been converted.
-        nb.nbformat = 3
+        nb.nbformat = nbformat
+        nb.nbformat_minor = nbformat_minor
+        
         nb.orig_nbformat = 2
         return nb
     elif orig_version == 3:
+        if orig_minor != nbformat_minor:
+            nb.orig_nbformat_minor = orig_minor
+        nb.nbformat_minor = nbformat_minor
         return nb
     else:
         raise ValueError('Cannot convert a notebook from v%s to v3' % orig_version)
diff --git a/IPython/nbformat/v3/nbbase.py b/IPython/nbformat/v3/nbbase.py
index 6e990f8..f4e312b 100644
--- a/IPython/nbformat/v3/nbbase.py
+++ b/IPython/nbformat/v3/nbbase.py
@@ -31,7 +31,8 @@ from IPython.utils.ipstruct import Struct
 #-----------------------------------------------------------------------------
 
 # Change this when incrementing the nbformat version
-nbformat = 3.0
+nbformat = 3
+nbformat_minor = 0
 
 class NotebookNode(Struct):
     pass
@@ -158,6 +159,7 @@ def new_notebook(name=None, metadata=None, worksheets=None):
     """Create a notebook by name, id and a list of worksheets."""
     nb = NotebookNode()
     nb.nbformat = nbformat
+    nb.nbformat_minor = nbformat_minor
     if worksheets is None:
         nb.worksheets = []
     else: