diff --git a/prebuilt.py b/prebuilt.py
index d3d41fd5da..8a14ad2f1f 100755
--- a/prebuilt.py
+++ b/prebuilt.py
@@ -120,10 +120,11 @@ def GetVersion():
 
 
 def LoadPrivateFilters(build_path):
-  """Load a file with keywords on a per line basis.
+  """Load private filters based on ebuilds found under _PRIVATE_OVERLAY_DIR.
 
+  This function adds filters to the global set _FILTER_PACKAGES.
   Args:
-    filter_file: file to load into _FILTER_PACKAGES
+    build_path: Path that _PRIVATE_OVERLAY_DIR is in.
   """
   # TODO(scottz): eventually use manifest.xml to find the proper
   # private overlay path.
diff --git a/prebuilt_unittest.py b/prebuilt_unittest.py
index 73bca566f5..d6bf886844 100755
--- a/prebuilt_unittest.py
+++ b/prebuilt_unittest.py
@@ -122,12 +122,8 @@ class TestPrebuiltFilters(unittest.TestCase):
   def testEmptyFiltersErrors(self):
     """Ensure LoadPrivateFilters errors if an empty list is generated."""
     os.makedirs(os.path.join(self.tmp_dir, prebuilt._PRIVATE_OVERLAY_DIR))
-    try:
-      prebuilt.LoadPrivateFilters(self.tmp_dir)
-    except prebuilt.FiltersEmpty:
-      return
-
-    self.fail('Exception was not raised for empty list')
+    self.assertRaises(prebuilt.FiltersEmpty, prebuilt.LoadPrivateFilters,
+                      self.tmp_dir)
 
 
 class TestPrebuilt(unittest.TestCase):