diff --git a/spackbot/helpers.py b/spackbot/helpers.py
index 1103959..7e3af6c 100644
--- a/spackbot/helpers.py
+++ b/spackbot/helpers.py
@@ -41,9 +41,9 @@
 pr_mirror_base_url = os.environ.get(
     "PR_BINARIES_MIRROR_BASE_URL", "s3://spack-binaries-prs"
 )
-shared_pr_mirror_retire_after_days = os.environ.get(
+shared_pr_mirror_retire_after_days = int(os.environ.get(
     "SHARED_PR_MIRROR_RETIRE_AFTER_DAYS", 7
-)
+))
 pr_shared_mirror = "shared_pr_mirror"
 pr_expected_base = os.environ.get("PR_BINARIES_BASE_BRANCH", "develop")