diff --git a/swh/lister/cran/lister.py b/swh/lister/cran/lister.py
index 9edd35a..3a46acf 100644
--- a/swh/lister/cran/lister.py
+++ b/swh/lister/cran/lister.py
@@ -41,7 +41,7 @@ def compute_package_url(repo: Mapping[str, str]) -> str:
 
     """
     return 'https://cran.r-project.org/src/contrib' \
-        '/%(Package)s_%(Version)s.tar.gz'.format(repo)
+        '/{Package}_{Version}.tar.gz'.format(**repo)
 
 
 class CRANLister(SimpleLister):