diff --git a/__init__.py b/__init__.py
index 2170be4..e646c0d 100644
--- a/__init__.py
+++ b/__init__.py
@@ -21,8 +21,16 @@ class Storage:
 		self._buildindex()
 
 	def _filepaths(self):
+		'''Iterates over all the files in the torrent.
+
+		Each item is a tuple of:
+			array of file path components (undecoded)
+			a pathlib.PurePath for the file
+			a pathlib.Path for file on disk
+		'''
+
 		for curfile in self._files:
-			fname = pathlib.Path(
+			fname = pathlib.PurePath(
 			    *(x.decode(self._encoding) for x in
 			    curfile['path']))
 			curfilepath = self._rootpath / fname
@@ -34,7 +42,8 @@ class Storage:
 			yield curfilepath
 
 	def _buildindex(self):
-		self._index = []
+		self._pieceindex = []
+		self._fileindex = {}
 		files = self._filepaths()
 		left = 0
 		curfile = None
@@ -50,7 +59,9 @@ class Storage:
 
 			if left == 0:
 				current = []
-				self._index.append(current)
+				self._fileindex.setdefault(fname,
+				    []).append(len(self._pieceindex))
+				self._pieceindex.append(current)
 				left = self._piecelen
 
 			sz = min(curfile['length'] - curfileoff, left)
@@ -61,12 +72,15 @@ class Storage:
 			curfileoff += sz
 			left -= sz
 
+	def filepieces(self):
+		return self._fileindex.items()
+
 	def filesforpiece(self, idx):
-		for x in self._index[idx]:
+		for x in self._pieceindex[idx]:
 			yield x['file']
 
 	def apply_piece(self, idx, fun):
-		for i in self._index[idx]:
+		for i in self._pieceindex[idx]:
 			with open(i['file'], 'rb') as fp:
 				fp.seek(i['offset'])
 				fun(fp.read(i['size']))
@@ -83,7 +97,8 @@ def validate(torrent, basedir):
 
 	torrentdir = basedir / info['name'].decode(encoding)
 
-	stor = Storage(torrentdir, info['files'], info['piece length'], encoding)
+	stor = Storage(torrentdir, info['files'], info['piece length'],
+	    encoding)
 
 	pieces = info['pieces']
 	piecescnt = len(pieces) // 20
@@ -102,10 +117,8 @@ def validate(torrent, basedir):
 	# if any piece of a file is bad, it's bad
 	allfiles = set(stor.allfiles())
 
-	badpieces = [ x for x, v in enumerate(valid) if not v ]
-
-	badfiles = reduce(set.__or__, (set(stor.filesforpiece(x)) for x in
-	    badpieces), set())
+	badfiles = { torrentdir / x for x, y in stor.filepieces() if
+	    not all(valid[i] for i in y) }
 
 	return allfiles - badfiles, badfiles
 
@@ -198,5 +211,7 @@ class _TestCases(unittest.TestCase):
 
 		val, inval = validate(self.torrent, self.basetempdir)
 
-		self.assertEqual(set(val), { sd / x for x in missingfiles.keys() if x not in badfiles })
-		self.assertEqual(set(inval), { sd / x for x in badfiles.keys() })
+		self.assertEqual(set(val), { sd / x for x in
+		    missingfiles.keys() if x not in badfiles })
+		self.assertEqual(set(inval), { sd / x for x in
+		    badfiles.keys() })