diff --git a/check_domain_expiration_rdap.py b/check_domain_expiration_rdap.py
index beb1995..631746b 100755
--- a/check_domain_expiration_rdap.py
+++ b/check_domain_expiration_rdap.py
@@ -255,8 +255,14 @@ def main():
         )
 
     domain = pyunycode.convert(args.domain)
+    # be sure that the provided server url ends with / for future concat
+    if args.server is not None:
+        if args.server[-1] != '/':
+            server = args.server + '/'
+        else:
+            server = args.server
     check = nagiosplugin.Check(
-        Expiration(domain, args.server),
+        Expiration(domain, server),
         nagiosplugin.ScalarContext(
             'daystoexpiration',
             warning=wrange,