diff --git a/pungi/phases/pkgset/pkgsets.py b/pungi/phases/pkgset/pkgsets.py
index 8786015e..aff893e0 100644
--- a/pungi/phases/pkgset/pkgsets.py
+++ b/pungi/phases/pkgset/pkgsets.py
@@ -236,12 +236,17 @@ class PackageSetBase(kobo.log.LoggingBase):
                         rpm_path = rpm_path[len(remove_path_prefix):]
                     f.write("%s\n" % rpm_path)
 
-    def load_old_file_cache(self, file_path):
+    @staticmethod
+    def load_old_file_cache(file_path):
         """
         Loads the cached FileCache stored in pickle format in `file_path`.
         """
         with open(file_path, "rb") as f:
-            self.old_file_cache = pickle.load(f)
+            return pickle.load(f)
+
+    def set_old_file_cache(self, old_file_cache):
+        """Set cache of old files."""
+        self.old_file_cache = old_file_cache
 
     def save_file_cache(self, file_path):
         """
diff --git a/pungi/phases/pkgset/sources/source_koji.py b/pungi/phases/pkgset/sources/source_koji.py
index 640e2fb5..90300a65 100644
--- a/pungi/phases/pkgset/sources/source_koji.py
+++ b/pungi/phases/pkgset/sources/source_koji.py
@@ -617,10 +617,16 @@ def populate_global_pkgset(compose, koji_wrapper, path_prefix, event):
         global_pkgset = pungi.phases.pkgset.pkgsets.KojiPackageSet(
             koji_wrapper, compose.conf["sigkeys"], logger=compose._logger,
             arches=all_arches)
+
         old_file_cache_path = _find_old_file_cache_path(compose)
+        old_file_cache = None
         if old_file_cache_path:
             compose.log_info("Reusing old PKGSET file cache from %s" % old_file_cache_path)
-            global_pkgset.load_old_file_cache(old_file_cache_path)
+            old_file_cache = pungi.phases.pkgset.pkgsets.KojiPackageSet.load_old_file_cache(
+                old_file_cache_path
+            )
+            global_pkgset.set_old_file_cache(old_file_cache)
+
         # Get package set for each compose tag and merge it to global package
         # list. Also prepare per-variant pkgset, because we do not have list
         # of binary RPMs in module definition - there is just list of SRPMs.
@@ -638,8 +644,8 @@ def populate_global_pkgset(compose, koji_wrapper, path_prefix, event):
                 populate_only_packages=populate_only_packages_to_gather,
                 cache_region=compose.cache_region,
                 extra_builds=extra_builds)
-            if old_file_cache_path:
-                pkgset.load_old_file_cache(old_file_cache_path)
+            if old_file_cache:
+                pkgset.set_old_file_cache(old_file_cache)
             # Create a filename for log with package-to-tag mapping. The tag
             # name is included in filename, so any slashes in it are replaced
             # with underscores just to be safe.