diff --git a/3rd_party_apps/sendfile/__init__.py b/3rd_party_apps/sendfile/__init__.py
index 9d7ce68ad2..eea11a74d8 100644
--- a/3rd_party_apps/sendfile/__init__.py
+++ b/3rd_party_apps/sendfile/__init__.py
@@ -4,6 +4,8 @@ __version__ = '.'.join(map(str, VERSION))
 import os.path
 from mimetypes import guess_type
 
+from django.http import Http404
+
 def _lazy_load(fn):
     _cached = []
     def _decorated():
@@ -19,7 +21,7 @@ def _get_sendfile():
     from django.conf import settings
     from django.core.exceptions import ImproperlyConfigured
 
-    backend = getattr(settings, 'SENDFILE_BACKEND', 'sendfile.backends.simple')
+    backend = getattr(settings, 'SENDFILE_BACKEND', None)
     if not backend:
         raise ImproperlyConfigured('You must specify a valued for SENDFILE_BACKEND')
     module = import_module(backend)
@@ -36,16 +38,22 @@ def sendfile(request, filename, attachment=False, attachment_filename=None):
     will typically prompt the user to download the file, rather than view it.
     '''
     _sendfile = _get_sendfile()
-    response = _sendfile(request, filename)
+
+    if not os.path.exists(filename):
+        raise Http404('"%s" does not exist' % filename)
+
+    mimetype, encoding = guess_type(filename)
+    if mimetype is None:
+        mimetype = 'application/octet-stream'
+        
+    response = _sendfile(request, filename, mimetype=mimetype)
     if attachment:
         attachment_filename = attachment_filename or os.path.basename(filename)
         response['Content-Disposition'] = 'attachment; filename=%s' % attachment_filename
 
     response['Content-length'] = os.path.getsize(filename)
-
-    content_type = guess_type(filename)[0]
-    if content_type is None:
-        content_type = "application/octet-stream"
-    response['Content-Type'] = content_type
+    response['Content-Type'] = mimetype
+    if encoding:
+        response['Content-Encoding'] = encoding
 
     return response
diff --git a/3rd_party_apps/sendfile/backends/development.py b/3rd_party_apps/sendfile/backends/development.py
index 5fa2221188..08a7dd0a42 100644
--- a/3rd_party_apps/sendfile/backends/development.py
+++ b/3rd_party_apps/sendfile/backends/development.py
@@ -2,7 +2,7 @@ from django.views.static import serve
 
 import os.path
 
-def sendfile(request, filename):
+def sendfile(request, filename, **kwargs):
     '''
     Send file using django dev static file server.
 
diff --git a/3rd_party_apps/sendfile/backends/mod_wsgi.py b/3rd_party_apps/sendfile/backends/mod_wsgi.py
index 82cf55c806..b8bdfc58d1 100644
--- a/3rd_party_apps/sendfile/backends/mod_wsgi.py
+++ b/3rd_party_apps/sendfile/backends/mod_wsgi.py
@@ -18,7 +18,7 @@ def _convert_file_to_url(filename):
 
     return u''.join(url)
 
-def sendfile(request, filename):
+def sendfile(request, filename, **kwargs):
     response = HttpResponse()
     response['Location'] = _convert_file_to_url(filename)
     # need to destroy get_host() to stop django
diff --git a/3rd_party_apps/sendfile/backends/simple.py b/3rd_party_apps/sendfile/backends/simple.py
index d65e8d6b9a..e74eeeb8b0 100644
--- a/3rd_party_apps/sendfile/backends/simple.py
+++ b/3rd_party_apps/sendfile/backends/simple.py
@@ -1,6 +1,56 @@
-from django.core.servers.basehttp import FileWrapper
-from django.http import HttpResponse
+import os
+import stat
+import re
+from email.Utils import parsedate_tz, mktime_tz
+
+from django.core.files.base import File
+from django.http import HttpResponse, HttpResponseNotModified
+from django.utils.http import http_date
+
+def sendfile(request, filename, **kwargs):
+    # Respect the If-Modified-Since header.
+    statobj = os.stat(filename)
+    mimetype = kwargs.get('mimetype', 'application/octet-stream')
+
+    if not was_modified_since(request.META.get('HTTP_IF_MODIFIED_SINCE'),
+                              statobj[stat.ST_MTIME], statobj[stat.ST_SIZE]):
+        return HttpResponseNotModified(mimetype=mimetype)
+    
+    
+    response = HttpResponse(File(file(filename, 'rb')))
+
+    response["Last-Modified"] = http_date(statobj[stat.ST_MTIME])
+    return response
+    
+def was_modified_since(header=None, mtime=0, size=0):
+    """
+    Was something modified since the user last downloaded it?
+
+    header
+      This is the value of the If-Modified-Since header.  If this is None,
+      I'll just return True.
+
+    mtime
+      This is the modification time of the item we're talking about.
+
+    size
+      This is the size of the item we're talking about.
+    """
+    try:
+        if header is None:
+            raise ValueError
+        matches = re.match(r"^([^;]+)(; length=([0-9]+))?$", header,
+                           re.IGNORECASE)
+        header_date = parsedate_tz(matches.group(1))
+        if header_date is None:
+            raise ValueError
+        header_mtime = mktime_tz(header_date)
+        header_len = matches.group(3)
+        if header_len and int(header_len) != size:
+            raise ValueError
+        if mtime > header_mtime:
+            raise ValueError
+    except (AttributeError, ValueError, OverflowError):
+        return True
+    return False
 
-def sendfile(request, filename):
-    wrapper = FileWrapper(file(filename))
-    return HttpResponse(wrapper)
diff --git a/3rd_party_apps/sendfile/backends/xsendfile.py b/3rd_party_apps/sendfile/backends/xsendfile.py
index 5bba6a3759..b0f2720f60 100644
--- a/3rd_party_apps/sendfile/backends/xsendfile.py
+++ b/3rd_party_apps/sendfile/backends/xsendfile.py
@@ -1,6 +1,6 @@
 from django.http import HttpResponse
 
-def sendfile(request, filename):
+def sendfile(request, filename, **kwargs):
     response = HttpResponse()
     response['X-Sendfile'] = filename