diff --git a/mbuild/port.py b/mbuild/port.py
index 0629c2347..a8f01feb2 100644
--- a/mbuild/port.py
+++ b/mbuild/port.py
@@ -174,7 +174,7 @@ def access_labels(self):
                 for label in port_labels:
                     access_labels.add(f"['{label}']")
             for label in itertools.product(referrer_labels, port_labels):
-                access_labels.add(f"['{"']['".join(label)}']")
+                access_labels.add("['{}']".format("']['".join(label)))
 
         for key, val in self.root.labels.items():
             if self is val: