diff --git a/test/test_util.py b/test/test_util.py
index 7da9be2f5..93c4b7ee6 100644
--- a/test/test_util.py
+++ b/test/test_util.py
@@ -14,37 +14,64 @@ class TestGeneratorFile(unittest.TestCase):
 
   def test_basic_generator(self):
     with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals(0, f.tell())
       self.assertEquals("thisisatest", f.read())
+      self.assertEquals(len("thisisatest"), f.tell())
 
   def test_same_lengths(self):
     with GeneratorFile(self.sample_generator()) as f:
       self.assertEquals("this", f.read(4))
+      self.assertEquals(4, f.tell())
+
       self.assertEquals("is", f.read(2))
+      self.assertEquals(6, f.tell())
+
       self.assertEquals("a", f.read(1))
+      self.assertEquals(7, f.tell())
+
       self.assertEquals("test", f.read(4))
+      self.assertEquals(11, f.tell())
 
   def test_indexed_lengths(self):
     with GeneratorFile(self.sample_generator()) as f:
       self.assertEquals("thisis", f.read(6))
+      self.assertEquals(6, f.tell())
+
       self.assertEquals("atest", f.read(5))
+      self.assertEquals(11, f.tell())
 
   def test_misindexed_lengths(self):
     with GeneratorFile(self.sample_generator()) as f:
       self.assertEquals("thisis", f.read(6))
+      self.assertEquals(6, f.tell())
+
       self.assertEquals("ate", f.read(3))
+      self.assertEquals(9, f.tell())
+
       self.assertEquals("st", f.read(2))
+      self.assertEquals(11, f.tell())
+
       self.assertEquals("", f.read(2))
+      self.assertEquals(11, f.tell())
 
   def test_misindexed_lengths_2(self):
     with GeneratorFile(self.sample_generator()) as f:
       self.assertEquals("thisisat", f.read(8))
+      self.assertEquals(8, f.tell())
+
       self.assertEquals("e", f.read(1))
+      self.assertEquals(9, f.tell())
+
       self.assertEquals("st", f.read(2))
+      self.assertEquals(11, f.tell())
+
       self.assertEquals("", f.read(2))
+      self.assertEquals(11, f.tell())
 
   def test_overly_long(self):
     with GeneratorFile(self.sample_generator()) as f:
       self.assertEquals("thisisatest", f.read(60))
+      self.assertEquals(11, f.tell())
 
 
 class TestUsernameGenerator(unittest.TestCase):
diff --git a/util/registry/generatorfile.py b/util/registry/generatorfile.py
index 36544cc28..e7d2bb657 100644
--- a/util/registry/generatorfile.py
+++ b/util/registry/generatorfile.py
@@ -10,10 +10,16 @@ class GeneratorFile(object):
     self._generator = generator
     self._closed = False
     self._buf = ''
+    self._position = 0
 
   def __iter__(self):
     return self
 
+  def tell(self):
+    """Return the file's current position, like stdio's ftell()."""
+    _complain_ifclosed(self._closed)
+    return self._position
+
   def next(self):
     """A file object is its own iterator, for example iter(f) returns f
     (unless f is closed). When a file is used as an iterator, typically
@@ -62,8 +68,11 @@ class GeneratorFile(object):
       self._buf = ''
       returned = buf
 
+    self._position = self._position + len(returned)
     return returned
 
+  def seek(self):
+    raise NotImplementedError
 
   def close(self):
     self._closed = True