diff --git a/compiler/router/supply_tree_router.py b/compiler/router/supply_tree_router.py
index c991ba34..e95cdee1 100644
--- a/compiler/router/supply_tree_router.py
+++ b/compiler/router/supply_tree_router.py
@@ -34,7 +34,8 @@ class supply_tree_router(router):
         # The pin escape router already made the bounding box big enough,
         # so we can use the regular bbox here.
         if pin_type:
-            debug.check(pin_type in ["left", "right", "top", "bottom", "ring"], "Invalid pin type {}".format(pin_type))
+            debug.check(pin_type in ["left", "right", "top", "bottom", "tree", "ring"],
+                        "Invalid pin type {}".format(pin_type))
         self.pin_type = pin_type
         router.__init__(self,
                         layers,