diff --git a/CHANGES.txt b/CHANGES.txt
index 8af21bd..2c87915 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
-May 28, 2013 - Added jp2 boxes to rst docs, XMLBox.indent method made private.
+May 30, 2013 - Added jp2 boxes to rst docs, XMLBox.indent method made private.
+    Precinct sizes must be multiples of two.
 
 May 27, 2013 - v0.1.1, Changed write example to not rely on matplotlib.  Fixed
     readthedocs.org setup to build documentation automatically.  Can import 
diff --git a/glymur/jp2k.py b/glymur/jp2k.py
index 6eb23fd..5c7e361 100644
--- a/glymur/jp2k.py
+++ b/glymur/jp2k.py
@@ -8,6 +8,7 @@ if sys.hexversion >= 0x03030000:
 else:
     from contextlib2 import ExitStack
 import ctypes
+import math
 import os
 import struct
 import warnings
@@ -181,7 +182,8 @@ class Jp2k(Jp2kBox):
         psnr : list, optional
             Different PSNR for successive layers.
         psizes : list, optional
-            List of precinct sizes.
+            List of precinct sizes.  Each precinct size tuple is defined in
+            (height x width).
         sop : bool, optional
             If true, write SOP marker before each packet.
         subsam : tuple, optional
@@ -266,9 +268,15 @@ class Jp2k(Jp2kBox):
             cparams.cp_fixed_quality = 1
 
         if psizes is not None:
-            for j, precinct in enumerate(psizes):
-                cparams.prcw_init[j] = precinct[0]
-                cparams.prch_init[j] = precinct[1]
+            for j, (prch, prcw) in enumerate(psizes):
+                if ((math.log(prch, 2) != math.floor(math.log(prch, 2)) or
+                     math.log(prcw, 2) != math.floor(math.log(prcw, 2)))):
+                    msg = "Bad precinct size ({0}, {1}), "
+                    msg += "must be multiple of 2."
+                    raise IOError(msg.format(prch, prcw))
+
+                cparams.prcw_init[j] = prcw
+                cparams.prch_init[j] = prch
             cparams.csty |= 0x01
             cparams.res_spec = len(psizes)
 
diff --git a/glymur/test/test_jp2k.py b/glymur/test/test_jp2k.py
index ae6af19..ff46d8c 100644
--- a/glymur/test/test_jp2k.py
+++ b/glymur/test/test_jp2k.py
@@ -53,7 +53,7 @@ class TestJp2k(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
         jp2file = pkg_resources.resource_filename(glymur.__name__,
-                                                       "data/nemo.jp2")
+                                                  "data/nemo.jp2")
         with tempfile.NamedTemporaryFile(suffix='.jp2', delete=False) as tfile:
             cls._bad_xml_file = tfile.name
             with open(jp2file, 'rb') as ifile:
diff --git a/glymur/test/test_opj_suite_neg.py b/glymur/test/test_opj_suite_neg.py
index 8296861..f33b981 100644
--- a/glymur/test/test_opj_suite_neg.py
+++ b/glymur/test/test_opj_suite_neg.py
@@ -9,6 +9,7 @@ import unittest
 import warnings
 
 import numpy as np
+import pkg_resources
 
 from ..lib import openjp2 as opj2
 
@@ -62,7 +63,8 @@ def read_image(infile):
 class TestSuiteNegative(unittest.TestCase):
 
     def setUp(self):
-        pass
+        self.jp2file = pkg_resources.resource_filename(glymur.__name__,
+                                                       "data/nemo.jp2")
 
     def tearDown(self):
         pass
@@ -150,5 +152,14 @@ class TestSuiteNegative(unittest.TestCase):
         with self.assertWarns(UserWarning) as cw:
             j = Jp2k(infile)
 
+    def test_precinct_size_not_multiple_of_two(self):
+        # Seems like precinct size should be a multiple of two.
+        ifile = Jp2k(self.jp2file)
+        data = ifile.read(reduce=3)
+        with tempfile.NamedTemporaryFile(suffix='.jp2') as tfile:
+            ofile = Jp2k(tfile.name, 'wb')
+            with self.assertRaises(IOError) as ce:
+                ofile.write(data, psizes=[(13, 13)])
+
 if __name__ == "__main__":
     unittest.main()