diff --git a/swh/graph/graph.py b/swh/graph/graph.py
--- a/swh/graph/graph.py
+++ b/swh/graph/graph.py
@@ -83,19 +83,19 @@
     def leaves(self, *args, **kwargs):
         yield from self.simple_traversal("leaves", *args, **kwargs)
 
-    def visit_nodes(self, direction="forward", edges="*", max_edges=None):
+    def visit_nodes(self, direction="forward", edges="*", max_edges=0):
         for node in call_async_gen(
             self.graph.backend.visit_nodes, direction, edges, self.id, max_edges
         ):
             yield self.graph[node]
 
-    def visit_edges(self, direction="forward", edges="*", max_edges=None):
+    def visit_edges(self, direction="forward", edges="*", max_edges=0):
         for src, dst in call_async_gen(
             self.graph.backend.visit_edges, direction, edges, self.id, max_edges
         ):
             yield (self.graph[src], self.graph[dst])
 
-    def visit_paths(self, direction="forward", edges="*", max_edges=None):
+    def visit_paths(self, direction="forward", edges="*", max_edges=0):
         for path in call_async_gen(
             self.graph.backend.visit_paths, direction, edges, self.id, max_edges
         ):