diff --git a/conans/client/graph/graph.py b/conans/client/graph/graph.py
index 96170d65b97..e851093b3e7 100644
--- a/conans/client/graph/graph.py
+++ b/conans/client/graph/graph.py
@@ -381,7 +381,7 @@ def report_graph_error(self):
 
     def serialize(self):
         for i, n in enumerate(self.nodes):
-            n.id = i
+            n.id = str(i)
         result = OrderedDict()
         result["nodes"] = {n.id: n.serialize() for n in self.nodes}
         result["root"] = {self.root.id: repr(self.root.ref)}  # TODO: ref of consumer/virtual