diff --git a/packages/istanbul-lib-report/src/reports/cobertura/index.ts b/packages/istanbul-lib-report/src/reports/cobertura/index.ts
index ac569d7..1ff490b 100644
--- a/packages/istanbul-lib-report/src/reports/cobertura/index.ts
+++ b/packages/istanbul-lib-report/src/reports/cobertura/index.ts
@@ -115,13 +115,15 @@ class CoberturaReport extends ReportBase {
 
     this.xml!.openTag("methods");
     const fnMap = fileCoverage.fnMap;
+    const uniqueMethodName = createUniqueNamer();
     Object.entries(fnMap).forEach(([k, { name, decl, loc }]) => {
       const hits = fileCoverage.f[k];
       // Some versions of the instrumenter in the wild populate 'loc'
       // but not 'decl':
       const start = (decl || loc).start;
       this.xml!.openTag("method", {
-        name: escape(name),
+        // Jenkins rejects two <method> tags with the same name in one class.
+        name: escape(uniqueMethodName(name)),
         hits,
         signature: "()V", //fake out a no-args void return
       });
@@ -167,4 +169,39 @@ function asClassName(node: ReportNode): string {
   return node.getRelativeName().replace(/.*[\\/]/, "");
 }
 
+const ANONYMOUS_NAME = /^\(anonymous_(\d+)\)$/;
+
+/** Returns a namer that deduplicates method names within one class. */
+function createUniqueNamer() {
+  const used = new Set<string>();
+  return (name: string | undefined): string => {
+    const base = name || "(anonymous)";
+    if (!used.has(base)) {
+      used.add(base);
+      return base;
+    }
+
+    const anonMatch = ANONYMOUS_NAME.exec(base);
+    if (anonMatch) {
+      let i = Number(anonMatch[1]) + 1;
+      let next = `(anonymous_${i})`;
+      while (used.has(next)) {
+        i += 1;
+        next = `(anonymous_${i})`;
+      }
+      used.add(next);
+      return next;
+    }
+
+    let i = 2;
+    let next = `${base}_${i}`;
+    while (used.has(next)) {
+      i += 1;
+      next = `${base}_${i}`;
+    }
+    used.add(next);
+    return next;
+  };
+}
+
 export default CoberturaReport;
diff --git a/packages/istanbul-lib-report/test/reports/cobertura/index.test.ts b/packages/istanbul-lib-report/test/reports/cobertura/index.test.ts
index 7077033..5b25328 100644
--- a/packages/istanbul-lib-report/test/reports/cobertura/index.test.ts
+++ b/packages/istanbul-lib-report/test/reports/cobertura/index.test.ts
@@ -3,7 +3,15 @@ import { createRequire } from "node:module";
 import path from "node:path";
 
 import * as istanbulLibCoverage from "@vitest/istanbul-lib-coverage";
-import { afterAll as after, assert, beforeAll as before, beforeEach, describe, it } from "vitest";
+import {
+  afterAll as after,
+  assert,
+  beforeAll as before,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vitest";
 
 import * as istanbulLibReport from "../../../src/index";
 import { FileWriter } from "../../../src/index";
@@ -57,4 +65,85 @@ describe("CoberturaReport", () => {
       createTest(file);
     }
   });
+
+  it("emits unique method names when fnMap has collisions", () => {
+    const context = istanbulLibReport.createContext({
+      dir: "./",
+      coverageMap: istanbulLibCoverage.createCoverageMap({
+        "/tmp/models.js": {
+          path: "/tmp/models.js",
+          statementMap: {},
+          fnMap: {
+            0: {
+              name: "constructor",
+              decl: {
+                start: { line: 2, column: 4 },
+                end: { line: 2, column: 20 },
+              },
+              loc: {
+                start: { line: 2, column: 4 },
+                end: { line: 4, column: 5 },
+              },
+              line: 2,
+            },
+            1: {
+              name: "constructor",
+              decl: {
+                start: { line: 8, column: 4 },
+                end: { line: 8, column: 20 },
+              },
+              loc: {
+                start: { line: 8, column: 4 },
+                end: { line: 10, column: 5 },
+              },
+              line: 8,
+            },
+            2: {
+              name: "(anonymous_0)",
+              decl: {
+                start: { line: 12, column: 0 },
+                end: { line: 12, column: 10 },
+              },
+              loc: {
+                start: { line: 12, column: 0 },
+                end: { line: 14, column: 1 },
+              },
+              line: 12,
+            },
+            3: {
+              name: "(anonymous_0)",
+              decl: {
+                start: { line: 16, column: 0 },
+                end: { line: 16, column: 10 },
+              },
+              loc: {
+                start: { line: 16, column: 0 },
+                end: { line: 18, column: 1 },
+              },
+              line: 16,
+            },
+          },
+          branchMap: {},
+          s: {},
+          f: { 0: 1, 1: 1, 2: 1, 3: 1 },
+          b: {},
+        },
+      }),
+    });
+    const tree = context.getTree("pkg");
+    const report = new CoberturaReport({
+      file: "-",
+      timestamp: "123456789",
+      projectRoot: "/tmp",
+    });
+    tree.visit(report, context);
+    const output = FileWriter.getOutput();
+    const names: string[] = [];
+    const re = /<method name="([^"]+)"/g;
+    let match: RegExpExecArray | null;
+    while ((match = re.exec(output))) {
+      names.push(match[1]);
+    }
+    expect(names).toEqual(["constructor", "constructor_2", "(anonymous_0)", "(anonymous_1)"]);
+  });
 });