diff --git a/backendspawner/backendspawner.py b/backendspawner/backendspawner.py
index 814e682..9313149 100644
--- a/backendspawner/backendspawner.py
+++ b/backendspawner/backendspawner.py
@@ -92,13 +92,26 @@ def get_request_kwargs(self):
             request_kwargs = self.request_kwargs
         return request_kwargs
 
-    port = Union(
+    custom_port = Union(
         [Integer(), Callable()],
         default_value=8080,
         help="""
         """,
     ).tag(config=True)
 
+    port = Integer(
+        help="""
+        The port for single-user servers to listen on.
+        """,
+    )
+
+    @default('port')
+    def get_port(self):
+        port = self.custom_port
+        if callable(port):
+            port = port()
+        return port
+
     async def get_port(self):
         if callable(self.port):
             port = await maybe_future(self.port(self))