diff --git a/compiler/router/graph.py b/compiler/router/graph.py
index cc6890cd..4a058fc9 100644
--- a/compiler/router/graph.py
+++ b/compiler/router/graph.py
@@ -50,7 +50,7 @@ class graph:
         This function assumes that p1 and p2 are on the same layer.
         """
 
-        probe_shape = graph_probe(p1, p2, self.router.vert_lpp if p1.z else self.router.horiz_lpp)
+        probe_shape = graph_probe(p1, p2, self.router.get_lpp(p1.z))
         # Check if any blockage blocks this probe
         for blockage in self.graph_blockages:
             # Check if two shapes overlap
diff --git a/compiler/router/router_tech.py b/compiler/router/router_tech.py
index 326a60a9..92366e3c 100644
--- a/compiler/router/router_tech.py
+++ b/compiler/router/router_tech.py
@@ -114,6 +114,14 @@ class router_tech:
         else:
             debug.error("Invalid zindex {}".format(zindex), -1)
 
+    def get_lpp(self, zindex):
+        if zindex == 1:
+            return self.vert_lpp
+        elif zindex == 0:
+            return self.horiz_lpp
+        else:
+            debug.error("Invalid zindex {}".format(zindex), -1)
+
     def get_layer_width_space(self, zindex):
         """
         These are the width and spacing of a supply layer given a supply rail