diff --git a/roles/tox/library/tox_install_sibling_packages.py b/roles/tox/library/tox_install_sibling_packages.py
index 4dd23b0c2..7d894f81a 100644
--- a/roles/tox/library/tox_install_sibling_packages.py
+++ b/roles/tox/library/tox_install_sibling_packages.py
@@ -106,7 +106,8 @@ def get_installed_packages(tox_python):
     frozen_pkgs = subprocess.check_output(
         [tox_python, '-m', 'pip', '-qqq', 'freeze']
     )
-    return [x.split('==')[0] for x in frozen_pkgs.split('\n') if '==' in x]
+    return [x[x.find('(') + 1:].split('==')[0]
+            for x in frozen_pkgs.split('\n') if '==' in x]
 
 
 def write_new_constraints_file(constraints, packages):