diff --git a/epdb/models.py b/epdb/models.py
index 324fe301..641caf2e 100644
--- a/epdb/models.py
+++ b/epdb/models.py
@@ -1573,14 +1573,12 @@ class Pathway(EnviPathModel, AliasMixin, ScenarioMixin):
         while len(queue):
             current = queue.pop()
             processed.add(current)
-
             nodes.append(current.d3_json())
 
-            for e in self.edges:
-                if current in e.start_nodes.all():
-                    for prod in e.end_nodes.all():
-                        if prod not in queue and prod not in processed:
-                            queue.append(prod)
+            for e in self.edges.filter(start_nodes=current).distinct():
+                for prod in e.end_nodes.all():
+                    if prod not in queue and prod not in processed:
+                        queue.append(prod)
 
         # We shouldn't lose or make up nodes...
         assert len(nodes) == len(self.nodes)