diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -99,7 +99,7 @@
 
     def run(self, portseed_offset):
         t = self.test_case
-        portseed = self.test_num + portseed_offset
+        portseed = self.test_num * 10 + portseed_offset
         portseed_arg = ["--portseed={}".format(portseed)]
         log_stdout = tempfile.SpooledTemporaryFile(max_size=2**16)
         log_stderr = tempfile.SpooledTemporaryFile(max_size=2**16)