diff --git a/glymur/core.py b/glymur/core.py
index 73a286e..6483558 100644
--- a/glymur/core.py
+++ b/glymur/core.py
@@ -74,6 +74,12 @@ _color_type_map_display = {
     _PRE_MULTIPLIED_OPACITY:  'pre-multiplied opacity',
     _UNSPECIFIED:  'unspecified'}
 
+# color channel definitions.
+RED = 1
+GREEN = 2
+BLUE = 3
+GREY = 1
+
 # enumerated color channel associations
 _rgb_colorspace = {"R": 1, "G": 2, "B": 3}
 _greyscale_colorspace = {"Y": 1}
diff --git a/glymur/jp2k.py b/glymur/jp2k.py
index d755cb0..846d7fd 100644
--- a/glymur/jp2k.py
+++ b/glymur/jp2k.py
@@ -16,8 +16,7 @@ import warnings
 import numpy as np
 
 from .codestream import Codestream
-from .core import progression_order
-from .core import SRGB
+from .core import *
 from .jp2box import *
 from .lib import openjp2 as opj2
 
@@ -467,6 +466,7 @@ class Jp2k(Jp2kBox):
         if len(colr_lst) == 0:
             msg = "The jp2 header box must contain a color definition box."
             raise IOError(msg)
+        colr = jp2h.box[colr_lst[0]]
 
         # Any cdef box must be in the jp2 header following the image header.
         cdef_lst = [j for (j, box) in enumerate(boxes) if box.id == 'cdef']
@@ -480,6 +480,21 @@ class Jp2k(Jp2kBox):
             msg = "Only one channel definition box is allowed in the "
             msg += "JP2 header."
             raise IOError(msg)
+        elif len(cdef_lst) == 1:
+            cdef = jp2h.box[cdef_lst[0]]
+            assn = cdef.association
+            typ = cdef.channel_type
+            index = cdef.index
+            if colr.colorspace == SRGB:
+                if any([chan + 1 not in assn or typ[chan] != 0 for chan in [0, 1, 2]]):
+                    msg = "All color channels must be defined in the "
+                    msg += "channel definition box."
+                    raise IOError(msg)
+            elif colr.colorspace == GREYSCALE:
+                if 0 not in typ:
+                    msg = "All color channels must be defined in the "
+                    msg += "channel definition box."
+                    raise IOError(msg)
 
         with open(filename, 'wb') as ofile:
             for box in boxes:
diff --git a/glymur/test/test_jp2box.py b/glymur/test/test_jp2box.py
index 89b66d1..59a241c 100644
--- a/glymur/test/test_jp2box.py
+++ b/glymur/test/test_jp2box.py
@@ -111,6 +111,19 @@ class TestChannelDefinition(unittest.TestCase):
             self.assertEqual(jp2h.box[2].channel_type, (0, 0, 0, 1))
             self.assertEqual(jp2h.box[2].association, (1, 2, 3, 0))
 
+    def test_bad_rgba(self):
+        """R, G, and B must be specified."""
+        j2k = Jp2k(self.four_planes)
+        cdef = glymur.jp2box.ChannelDefinitionBox(index=[0, 1, 2, 3],
+                                                  channel_type=[0, 0, 1, 1],
+                                                  association=[1, 2, 3, 0])
+        boxes = [self.ihdr, self.colr_rgb, cdef]
+        self.jp2h.box = boxes
+        boxes = [self.jP, self.ftyp, self.jp2h, self.jp2c]
+        with tempfile.NamedTemporaryFile(suffix=".jp2") as tfile:
+            with self.assertRaises(IOError) as ce:
+                j2k.wrap(tfile.name, boxes=boxes)
+
     def test_grey(self):
         """Just regular greyscale."""
         j2k = Jp2k(self.one_plane)
@@ -151,6 +164,21 @@ class TestChannelDefinition(unittest.TestCase):
             self.assertEqual(jp2h.box[2].channel_type, (0, 1))
             self.assertEqual(jp2h.box[2].association, (1, 0))
 
+    def test_bad_grey_alpha(self):
+        """A greyscale image with alpha layer must specify Y"""
+        j2k = Jp2k(self.two_planes)
+
+        # This cdef box 
+        cdef = glymur.jp2box.ChannelDefinitionBox(index=[0, 1],
+                                                  channel_type=[1, 1],
+                                                  association=[0, 1])
+        boxes = [self.ihdr, self.colr_gr, cdef]
+        self.jp2h.box = boxes
+        boxes = [self.jP, self.ftyp, self.jp2h, self.jp2c]
+        with tempfile.NamedTemporaryFile(suffix=".jp2") as tfile:
+            with self.assertRaises((OSError, IOError)) as ce:
+                j2k.wrap(tfile.name, boxes=boxes)
+
     def test_only_one_cdef_in_jp2_header(self):
         """There can only be one channel definition box in the jp2 header."""
         j2k = Jp2k(self.j2kfile)