diff --git a/src/calibre/gui2/tweak_book/editor/canvas.py b/src/calibre/gui2/tweak_book/editor/canvas.py
index 153b7d7af3..f51f9a3b86 100644
--- a/src/calibre/gui2/tweak_book/editor/canvas.py
+++ b/src/calibre/gui2/tweak_book/editor/canvas.py
@@ -14,7 +14,6 @@ from PyQt4.Qt import (
     QPointF, QPen, pyqtSignal, QUndoCommand, QUndoStack, QIcon, QImage, QByteArray)
 
 from calibre import fit_image
-from calibre.constants import isosx
 from calibre.gui2 import error_dialog, pixmap_to_data
 from calibre.gui2.dnd import (
     IMAGE_EXTENSIONS, dnd_has_extension, dnd_has_image, dnd_get_image, DownloadDialog)
@@ -94,13 +93,6 @@ def get_pixel_map():
 
 def qimage_to_magick(img):
     ans = Image()
-    if isosx:
-        # For some reson, on OSX MagickConstituteImage fails, and I can't be
-        # bothered figuring out why. Dumping to uncompressed PNG is reasonably
-        # fast.
-        raw = pixmap_to_data(img, 'PNG', quality=100)
-        ans.load(raw)
-        return ans
     fmt = get_pixel_map()
     if not img.hasAlphaChannel():
         if img.format() != img.Format_RGB32:
@@ -117,7 +109,7 @@ def qimage_to_magick(img):
 
 def magick_to_qimage(img):
     fmt = get_pixel_map()
-    # ImageMagick can output only output raw data in some formats that can be
+    # ImageMagick can only output raw data in some formats that can be
     # read into QImage directly, if the QImage format is not one of those, use
     # PNG
     if fmt in {'RGBA', 'BGRA'}:
diff --git a/src/calibre/utils/magick/magick.c b/src/calibre/utils/magick/magick.c
index 9aa04b4c96..ce1ccbf71f 100644
--- a/src/calibre/utils/magick/magick.c
+++ b/src/calibre/utils/magick/magick.c
@@ -540,14 +540,14 @@ magick_Image_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 // Image.constitute {{{
 static PyObject *
 magick_Image_constitute(magick_Image *self, PyObject *args) {
-    const char *map;
-	Py_ssize_t width, height;
-    PyObject *capsule;
-    MagickBooleanType res;
-    void *data;
+    const char *map = NULL;
+    unsigned int width = 0, height = 0;
+    PyObject *capsule = NULL;
+    MagickBooleanType res = MagickFalse;
+    void *data = NULL;
     
     NULL_CHECK(NULL)
-    if (!PyArg_ParseTuple(args, "iisO", &width, &height, &map, &capsule)) return NULL;
+    if (!PyArg_ParseTuple(args, "IIsO", &width, &height, &map, &capsule)) return NULL;
 
     if (!PyCapsule_CheckExact(capsule)) {
         PyErr_SetString(PyExc_TypeError, "data is not a capsule object");
@@ -557,7 +557,7 @@ magick_Image_constitute(magick_Image *self, PyObject *args) {
     data = PyCapsule_GetPointer(capsule,  PyCapsule_GetName(capsule));
     if (data == NULL) return NULL;
 
-    res = MagickConstituteImage(self->wand, width, height, map, CharPixel, data);
+    res = MagickConstituteImage(self->wand, (size_t)width, (size_t)height, map, CharPixel, data);
 
     if (!res)
         return magick_set_exception(self->wand);