diff --git a/backend/copr_backend/helpers.py b/backend/copr_backend/helpers.py
index f74f2aa4d..05348366d 100644
--- a/backend/copr_backend/helpers.py
+++ b/backend/copr_backend/helpers.py
@@ -634,11 +634,12 @@ def get_chroot_arch(chroot):
 
 def format_evr(epoch, version, release):
     """
-    Return evr in format (epoch:)version-release
+    Return evr in format (epoch:)version-release.  The argument 'epoch' should
+    be integer value or null (but we rather also consider "strings" values).
     """
-    if epoch is not None and epoch.isdigit():
-        return f"{epoch}:{version}-{release}"
-
+    if epoch is not None:
+        if isinstance(epoch, int) or epoch.isdigit():
+            return f"{epoch}:{version}-{release}"
     return f"{version}-{release}"