diff --git a/src/libprs500/__init__.py b/src/libprs500/__init__.py
index f1547982d4..159d14adf8 100644
--- a/src/libprs500/__init__.py
+++ b/src/libprs500/__init__.py
@@ -377,3 +377,35 @@ def launch(path_or_url):
     elif iswindows:
         import win32api
         win32api.ShellExecute(0, 'open', path_or_url, None, os.getcwd(), 1)
+        
+def relpath(target, base=os.curdir):
+    """
+    Return a relative path to the target from either the current dir or an optional base dir.
+    Base can be a directory specified either as absolute or relative to current dir.
+    """
+
+    if not os.path.exists(target):
+        raise OSError, 'Target does not exist: '+target
+
+    if not os.path.isdir(base):
+        raise OSError, 'Base is not a directory or does not exist: '+base
+
+    base_list = (os.path.abspath(base)).split(os.sep)
+    target_list = (os.path.abspath(target)).split(os.sep)
+
+    # On the windows platform the target may be on a completely different drive from the base.
+    if iswindows and base_list[0] <> target_list[0]:
+        raise OSError, 'Target is on a different drive to base. Target: '+target_list[0].upper()+', base: '+base_list[0].upper()
+
+    # Starting from the filepath root, work out how much of the filepath is
+    # shared by base and target.
+    for i in range(min(len(base_list), len(target_list))):
+        if base_list[i] <> target_list[i]: break
+    else:
+        # If we broke out of the loop, i is pointing to the first differing path elements.
+        # If we didn't break out of the loop, i is pointing to identical path elements.
+        # Increment i so that in all cases it points to the first differing path elements.
+        i+=1
+
+    rel_list = [os.pardir] * (len(base_list)-i) + target_list[i:]
+    return os.path.join(*rel_list)
diff --git a/src/libprs500/web/fetch/simple.py b/src/libprs500/web/fetch/simple.py
index 9fe122219f..3d115d4340 100644
--- a/src/libprs500/web/fetch/simple.py
+++ b/src/libprs500/web/fetch/simple.py
@@ -21,7 +21,7 @@ import sys, socket, os, urlparse, codecs, logging, re, time, copy, urllib2, thre
 from urllib import url2pathname
 from httplib import responses
 
-from libprs500 import setup_cli_handlers, browser, sanitize_file_name, OptionParser
+from libprs500 import setup_cli_handlers, browser, sanitize_file_name, OptionParser, relpath
 from libprs500.ebooks.BeautifulSoup import BeautifulSoup, Tag
 from libprs500.ebooks.chardet import xml_to_unicode
 
@@ -45,27 +45,12 @@ def save_soup(soup, target):
             meta.replaceWith(nm)
     
     selfdir = os.path.dirname(target)
-    def abs2rel(path, base):
-        prefix = os.path.commonprefix([path, base])
-        if not os.path.exists(prefix) or not os.path.isdir(prefix):
-            prefix = os.path.dirname(prefix)
-        prefix = os.path.normpath(prefix)
-        if prefix.startswith(selfdir): # path is in a subdirectory
-            return path[len(prefix)+1:]
-        from_prefix = path[len(prefix)+1:]
-        left = base
-        ups = []
-        while left != prefix:
-            left = os.path.split(left)[0]
-            ups.append('..')
-        ups.append(from_prefix)
-        return os.path.join(*ups)
     
     for tag in soup.findAll(['img', 'link', 'a']):
         for key in ('src', 'href'):
             path = tag.get(key, None)
             if path and os.path.exists(path) and os.path.isabs(path):
-                tag[key] = abs2rel(path, selfdir).replace(os.sep, '/')
+                tag[key] = relpath(path, selfdir).replace(os.sep, '/')
     
     f = codecs.open(target, 'w', 'utf-8')
     f.write(unicode(soup))