diff --git a/hugr-py/src/hugr/hugr.py b/hugr-py/src/hugr/hugr.py
index ea393a373..c98cdb6ad 100644
--- a/hugr-py/src/hugr/hugr.py
+++ b/hugr-py/src/hugr/hugr.py
@@ -138,7 +138,7 @@ def __iter__(self):
         return iter(self._nodes)
 
     def __len__(self) -> int:
-        return len(self._nodes) - len(self._free_nodes)
+        return self.num_nodes()
 
     def add_node(
         self,
@@ -155,15 +155,17 @@ def add_node(
             self._nodes.append(node_data)
         return node
 
-    def delete_node(self, node: Node) -> None:
+    def delete_node(self, node: Node) -> NodeData | None:
         for offset in range(self.num_in_ports(node)):
             self._links.delete_right(node.inp(offset))
         for offset in range(self.num_out_ports(node)):
             self._links.delete_left(node.out(offset))
+        weight = self._nodes[node.idx]
         self._nodes[node.idx] = None
         self._free_nodes.append(node)
+        return weight
 
-    def add_link(self, src: OutPort, dst: InPort, ty: Type | None = None) -> None:
+    def add_link(self, src: OutPort, dst: InPort) -> None:
         src = _unused_sub_offset(src, self._links)
         dst = _unused_sub_offset(dst, self._links)
         if self._links.get_left(dst) is not None:
@@ -173,6 +175,9 @@ def add_link(self, src: OutPort, dst: InPort, ty: Type | None = None) -> None:
     def delete_link(self, src: OutPort, dst: InPort) -> None:
         self._links.delete_left(src)
 
+    def num_nodes(self) -> int:
+        return len(self._nodes) - len(self._free_nodes)
+
     def num_in_ports(self, node: Node) -> int:
         return len(self.in_ports(node))
 
diff --git a/hugr-py/tests/test_hugr_build.py b/hugr-py/tests/test_hugr_build.py
index 03092b072..fe703d405 100644
--- a/hugr-py/tests/test_hugr_build.py
+++ b/hugr-py/tests/test_hugr_build.py
@@ -3,6 +3,7 @@
 from hugr.hugr import Dfg, Hugr, DummyOp, Node
 import hugr.serialization.tys as stys
 import hugr.serialization.ops as sops
+import pytest
 
 BOOL_T = stys.Type(stys.SumType(stys.UnitSum(size=2)))
 QB_T = stys.Type(stys.Qubit())
@@ -38,7 +39,6 @@
 
 
 def _validate(h: Hugr, mermaid: bool = False):
-    # TODO point to built hugr binary
     # cmd = ["cargo", "run", "--features", "cli", "--"]
     cmd = ["./target/debug/hugr"]
 
@@ -47,6 +47,38 @@ def _validate(h: Hugr, mermaid: bool = False):
     subprocess.run(cmd + ["-"], check=True, input=h.to_serial().to_json().encode())
 
 
+def test_stable_indices():
+    h = Hugr(DummyOp(sops.DFG(parent=-1)))
+
+    nodes = [h.add_node(NOT_OP) for _ in range(3)]
+    assert len(h) == 4
+
+    h.add_link(nodes[0].out(0), nodes[1].inp(0))
+
+    assert h.num_out_ports(nodes[0]) == 1
+    assert h.num_in_ports(nodes[1]) == 1
+
+    assert h.delete_node(nodes[1]) is not None
+
+    assert len(h) == 3
+    assert len(h._nodes) == 4
+    assert h._free_nodes == [nodes[1]]
+
+    assert h.num_out_ports(nodes[0]) == 0
+    assert h.num_in_ports(nodes[1]) == 0
+
+    with pytest.raises(KeyError):
+        _ = h[nodes[1]]
+    with pytest.raises(KeyError):
+        _ = h[Node(46)]
+
+    new_n = h.add_node(NOT_OP)
+    assert new_n == nodes[1]
+
+    assert len(h) == 4
+    assert h._free_nodes == []
+
+
 def test_simple_id():
     h = Dfg.endo([QB_T] * 2)
     a, b = h.inputs()