diff --git a/Tools/demo/rpython.py b/Tools/demo/rpython.py
index 8d7e2747636..11f72cb3dd2 100755
--- a/Tools/demo/rpython.py
+++ b/Tools/demo/rpython.py
@@ -19,7 +19,7 @@ def main():
     port = PORT
     i = host.find(':')
     if i >= 0:
-        port = int(port[i+1:])
+        port = int(host[i+1:])
         host = host[:i]
     command = ' '.join(sys.argv[2:])
     with socket(AF_INET, SOCK_STREAM) as s: