diff --git a/pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py b/pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py
index 3a6a14133ea3..59336cfae4a0 100755
--- a/pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py
+++ b/pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py
@@ -242,7 +242,9 @@ DEFAULT_SETUPTOOLS_EXTENSION = 'tar.gz'
 
 FORMATS = {
     'setuptools'        :   DEFAULT_SETUPTOOLS_EXTENSION,
-    'wheel'             :   'whl'
+    'wheel'             :   'whl',
+    'pyproject'         :   'tar.gz',
+    'flit'              :   'tar.gz'
 }
 
 def _determine_fetcher(text):
@@ -281,12 +283,8 @@ def _determine_extension(text, fetcher):
         if extension is None:
             if src_format is None:
                 src_format = 'setuptools'
-            elif src_format == 'flit':
-                raise ValueError("Don't know how to update a Flit package.")
             elif src_format == 'other':
                 raise ValueError("Don't know how to update a format='other' package.")
-            elif src_format == 'pyproject':
-                raise ValueError("Don't know how to update a pyproject package.")
             extension = FORMATS[src_format]
 
     elif fetcher == 'fetchurl':