diff --git a/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js b/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js
index 9422a5f37..6395940b0 100644
--- a/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js
+++ b/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js
@@ -1,8 +1,62 @@
+import { vi } from 'vitest';
+
 import * as configApi from '../../config';
 import mermaidAPI from '../../mermaidAPI';
 import Diagram from '../../Diagram';
 import { addDiagrams } from '../../diagram-api/diagram-orchestration';
+
+/**
+ * Sequence diagrams require their own very special version of a mocked d3 module
+ * diagrams/sequence/svgDraw uses statements like this with d3 nodes: (note the [0][0])
+ *
+ *   // in drawText(...)
+ *   textHeight += (textElem._groups || textElem)[0][0].getBBox().height;
+ */
+vi.mock('d3', () => {
+  const NewD3 = function () {
+    function returnThis() {
+      return this;
+    }
+    return {
+      append: function () {
+        return NewD3();
+      },
+      lower: returnThis,
+      attr: returnThis,
+      style: returnThis,
+      text: returnThis,
+      // [0][0] (below) is required by drawText() in packages/mermaid/src/diagrams/sequence/svgDraw.js
+      0: {
+        0: {
+          getBBox: function () {
+            return {
+              height: 10,
+              width: 20,
+            };
+          },
+        },
+      },
+    };
+  };
+
+  return {
+    select: function () {
+      return new NewD3();
+    },
+
+    selectAll: function () {
+      return new NewD3();
+    },
+
+    curveBasis: 'basis',
+    curveLinear: 'linear',
+    curveCardinal: 'cardinal',
+  };
+});
+// -------------------------------
+
 addDiagrams();
+
 /**
  * @param conf
  * @param key
diff --git a/packages/mermaid/src/diagrams/sequence/svgDraw.spec.js b/packages/mermaid/src/diagrams/sequence/svgDraw.spec.js
index 580dafe89..8e5f5f32b 100644
--- a/packages/mermaid/src/diagrams/sequence/svgDraw.spec.js
+++ b/packages/mermaid/src/diagrams/sequence/svgDraw.spec.js
@@ -1,5 +1,31 @@
+import { vi } from 'vitest';
 import svgDraw from './svgDraw';
-import { MockD3 } from 'd3';
+
+// This is the only place that uses this mock
+export const MockD3 = (name, parent) => {
+  const children = [];
+  const elem = {
+    get __children() {
+      return children;
+    },
+    get __name() {
+      return name;
+    },
+    get __parent() {
+      return parent;
+    },
+  };
+  elem.append = (name) => {
+    const mockElem = MockD3(name, elem);
+    children.push(mockElem);
+    return mockElem;
+  };
+  elem.lower = vi.fn(() => elem);
+  elem.attr = vi.fn(() => elem);
+  elem.text = vi.fn(() => elem);
+  elem.style = vi.fn(() => elem);
+  return elem;
+};
 
 describe('svgDraw', function () {
   describe('drawRect', function () {