diff --git a/.changeset/fix-7609-numeric-subgraph-id.md b/.changeset/fix-7609-numeric-subgraph-id.md
new file mode 100644
index 00000000000..301a9014265
--- /dev/null
+++ b/.changeset/fix-7609-numeric-subgraph-id.md
@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix(flowchart): render nested subgraphs with numeric ids without dagre rank crash (#7609)
diff --git a/cypress/integration/rendering/flowchart/flowchart.spec.js b/cypress/integration/rendering/flowchart/flowchart.spec.js
index 55cf02a7454..268ca74264d 100644
--- a/cypress/integration/rendering/flowchart/flowchart.spec.js
+++ b/cypress/integration/rendering/flowchart/flowchart.spec.js
@@ -1003,6 +1003,23 @@ graph TD
       }
     );
   });
+  it('#7609: should render nested subgraph with numeric id without crashing', () => {
+    imgSnapshotTest(
+      `
+      graph LR
+        subgraph outer
+          subgraph 1 ["inner"]
+            external
+            subgraph sub
+              internal
+            end
+            sub-->external
+          end
+        end
+      `,
+      { fontFamily: 'courier' }
+    );
+  });
 });
 it('#5824: should be able to render string and markdown labels', () => {
   imgSnapshotTest(
diff --git a/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.js b/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.js
index 7e5c5f582ff..1752e2446a2 100644
--- a/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.js
+++ b/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.js
@@ -363,6 +363,19 @@ export const extractor = (graph, depth) => {
   // containing the nodes and edges in the cluster in a new graph
   // for (let i = 0;)
   let nodes = graph.nodes();
+  // graphlib backs nodes with a plain object, so integer-like string ids
+  // ("1") sort ahead of others ("outer") and reorder iteration. Process
+  // outer clusters first so nested extraction is order-independent. (#7609)
+  const nodeDepth = (v) => {
+    let d = 0;
+    let cur = graph.parent(v);
+    while (cur != null) {
+      d++;
+      cur = graph.parent(cur);
+    }
+    return d;
+  };
+  nodes = [...nodes].sort((a, b) => nodeDepth(a) - nodeDepth(b));
   let hasChildren = false;
   for (const node of nodes) {
     const children = graph.children(node);
diff --git a/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.spec.js b/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.spec.js
index d44e5439110..b76041f309a 100644
--- a/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.spec.js
+++ b/packages/mermaid/src/dagre-wrapper/mermaid-graphlib.spec.js
@@ -373,6 +373,40 @@ describe('Graphlib decorations', () => {
       expect(bGraph.edges().length).toBe(0);
     });
   });
+  it('adjustClustersAndEdges should extract nested clusters when a subgraph has a numeric id (issue #7609)', function () {
+    /*
+      graph LR
+        subgraph outer
+          subgraph 1 ["inner"]
+            external
+            subgraph sub
+              internal
+            end
+            sub-->external
+          end
+        end
+    */
+    g.setNode('outer', { id: 'outer' });
+    g.setNode('1', { id: '1' });
+    g.setNode('sub', { id: 'sub' });
+    g.setNode('external', { id: 'external' });
+    g.setNode('internal', { id: 'internal' });
+    g.setParent('1', 'outer');
+    g.setParent('sub', '1');
+    g.setParent('external', '1');
+    g.setParent('internal', 'sub');
+    g.setEdge('sub', 'external', { data: 'sub-external' });
+
+    adjustClustersAndEdges(g);
+
+    const outerGraph = g.node('outer').graph;
+    const innerGraph = outerGraph.node('1').graph;
+    expect(innerGraph.node('sub')?.clusterNode).toBe(true);
+    const subGraph = innerGraph.node('sub').graph;
+    expect(subGraph.nodes()).toEqual(['internal']);
+    expect(innerGraph.children('sub')).toEqual([]);
+  });
+
   it('adjustClustersAndEdges should handle nesting GLB77', function () {
     /*
 flowchart TB
diff --git a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js
index ffe9062154f..48feed70f66 100644
--- a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js
+++ b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js
@@ -336,6 +336,19 @@ export const extractor = (graph, depth) => {
     return;
   }
   let nodes = graph.nodes();
+  // graphlib backs nodes with a plain object, so integer-like string ids
+  // ("1") sort ahead of others ("outer") and reorder iteration. Process
+  // outer clusters first so nested extraction is order-independent. (#7609)
+  const nodeDepth = (v) => {
+    let d = 0;
+    let cur = graph.parent(v);
+    while (cur != null) {
+      d++;
+      cur = graph.parent(cur);
+    }
+    return d;
+  };
+  nodes = [...nodes].sort((a, b) => nodeDepth(a) - nodeDepth(b));
   let hasChildren = false;
   for (const node of nodes) {
     const children = graph.children(node);
diff --git a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js
index 2e21b8ec4d9..12cf2e9562b 100644
--- a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js
+++ b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js
@@ -373,6 +373,40 @@ describe('Graphlib decorations', () => {
       expect(bGraph.edges().length).toBe(0);
     });
   });
+  it('adjustClustersAndEdges should extract nested clusters when a subgraph has a numeric id (issue #7609)', function () {
+    /*
+      graph LR
+        subgraph outer
+          subgraph 1 ["inner"]
+            external
+            subgraph sub
+              internal
+            end
+            sub-->external
+          end
+        end
+    */
+    g.setNode('outer', { id: 'outer' });
+    g.setNode('1', { id: '1' });
+    g.setNode('sub', { id: 'sub' });
+    g.setNode('external', { id: 'external' });
+    g.setNode('internal', { id: 'internal' });
+    g.setParent('1', 'outer');
+    g.setParent('sub', '1');
+    g.setParent('external', '1');
+    g.setParent('internal', 'sub');
+    g.setEdge('sub', 'external', { data: 'sub-external' });
+
+    adjustClustersAndEdges(g);
+
+    const outerGraph = g.node('outer').graph;
+    const innerGraph = outerGraph.node('1').graph;
+    expect(innerGraph.node('sub')?.clusterNode).toBe(true);
+    const subGraph = innerGraph.node('sub').graph;
+    expect(subGraph.nodes()).toEqual(['internal']);
+    expect(innerGraph.children('sub')).toEqual([]);
+  });
+
   it('adjustClustersAndEdges should handle nesting GLB77', function () {
     /*
 flowchart TB