diff --git a/.github/workflows/integration_tests.yml b/.github/workflows/integration_tests.yml
index e850b42a7..a00f86dcc 100644
--- a/.github/workflows/integration_tests.yml
+++ b/.github/workflows/integration_tests.yml
@@ -41,6 +41,7 @@ jobs:
             skip: --noFirefox
 
     runs-on: ${{ matrix.os }}
+    environment: code-coverage
 
     steps:
       - name: Checkout repository
@@ -75,13 +76,13 @@ jobs:
         if: ${{ matrix.os == 'windows-latest' }}
         run: Set-DisplayResolution -Width 1920 -Height 1080 -Force
 
-      - name: Run integration tests (Windows)
+      - name: Run integration tests with code coverage (Windows)
         if: ${{ matrix.os == 'windows-latest' }}
-        run: npx gulp integrationtest ${{ matrix.skip }}
+        run: npx gulp integrationtest --coverage --coverage-output build/coverage/integration ${{ matrix.skip }}
 
-      - name: Run integration tests (Linux)
+      - name: Run integration tests with code coverage (Linux)
         if: ${{ matrix.os == 'ubuntu-latest' }}
-        run: xvfb-run -a --server-args="-screen 0, 1920x1080x24" npx gulp integrationtest ${{ matrix.skip }}
+        run: xvfb-run -a --server-args="-screen 0, 1920x1080x24" npx gulp integrationtest --coverage --coverage-output build/coverage/integration ${{ matrix.skip }}
 
       - name: Save cached PDF files
         uses: actions/cache/save@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
@@ -89,3 +90,15 @@ jobs:
           path: test/pdfs/*.pdf
           key: cached-pdf-files-${{ hashFiles('test/pdfs/*.pdf') }}
           enableCrossOsArchive: true
+
+      - name: Upload results to Codecov
+        uses: codecov/codecov-action@57e3a136b779b570ffcdbf80b3bdc90e7fab3de2 # v6.0.0
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: true
+          files: ./build/coverage/integration/lcov.info
+          flags: integrationtest
+          name: codecov-umbrella
+          disable_search: true
+          disable_telem: true
+          verbose: true
diff --git a/src/core/worker.js b/src/core/worker.js
index 9dd67e783..e089f47d1 100644
--- a/src/core/worker.js
+++ b/src/core/worker.js
@@ -1036,6 +1036,9 @@ class WorkerMessageHandler {
           .getPage(data.pageIndex)
           .then(page => page.annotations.map(a => a.toString()));
       });
+      handler.on("GetWorkerCoverage", function () {
+        return globalThis.__coverage__ ?? {};
+      });
     }
 
     return workerHandlerName;
diff --git a/test/coverage_utils.js b/test/coverage_utils.js
index 118e63593..3222e224e 100644
--- a/test/coverage_utils.js
+++ b/test/coverage_utils.js
@@ -15,15 +15,15 @@
 
 // Istanbul coverage objects use s (statements), b (branches), and f (functions)
 // as shorthand keys for the hit-count maps.
-function mergeWorkerCoverageIntoWindow(coverage) {
+function mergeCoverageIntoGlobal(coverage) {
   if (!coverage || Object.keys(coverage).length === 0) {
     return;
   }
-  window.__coverage__ ??= {};
+  globalThis.__coverage__ ??= {};
   for (const [key, fileCoverage] of Object.entries(coverage)) {
-    const existing = window.__coverage__[key];
+    const existing = globalThis.__coverage__[key];
     if (!existing) {
-      window.__coverage__[key] = fileCoverage;
+      globalThis.__coverage__[key] = fileCoverage;
       continue;
     }
     for (const id of Object.keys(fileCoverage.s)) {
@@ -49,10 +49,10 @@ async function fetchAndMergeWorkerCoverage(pdfWorker) {
       "GetWorkerCoverage",
       null
     );
-    mergeWorkerCoverageIntoWindow(coverage);
+    mergeCoverageIntoGlobal(coverage);
   } catch (e) {
     console.warn(`Failed to collect worker coverage: ${e}`);
   }
 }
 
-export { fetchAndMergeWorkerCoverage, mergeWorkerCoverageIntoWindow };
+export { fetchAndMergeWorkerCoverage, mergeCoverageIntoGlobal };
diff --git a/test/integration/test_utils.mjs b/test/integration/test_utils.mjs
index b0c16f856..4146fcd7e 100644
--- a/test/integration/test_utils.mjs
+++ b/test/integration/test_utils.mjs
@@ -13,6 +13,7 @@
  * limitations under the License.
  */
 
+import { mergeCoverageIntoGlobal } from "../coverage_utils.js";
 import os from "os";
 
 const isMac = os.platform() === "darwin";
@@ -149,11 +150,42 @@ function closePages(pages) {
 }
 
 async function closeSinglePage(page) {
-  // Avoid to keep something from a previous test.
-  await page.evaluate(async () => {
+  const coverage = await page.evaluate(async () => {
+    // Collect coverage data from the worker before the document is closed.
+    let workerCoverage = null;
+    const handler =
+      window.PDFViewerApplication.pdfDocument?._transport?.messageHandler;
+    if (handler) {
+      try {
+        workerCoverage = await handler.sendWithPromise(
+          "GetWorkerCoverage",
+          null
+        );
+      } catch {}
+    }
+
+    // Close the viewer gracefully, and clear local storage to avoid state
+    // leaking from one test to another.
     await window.PDFViewerApplication.testingClose();
     window.localStorage.clear();
+
+    // Serialize the coverage data to a JSON string because that is a lot
+    // faster/cheaper to transfer from the browser to Node.js over the WebDriver
+    // BiDi protocol, otherwise Puppeteer's (significantly slower) serialization
+    // logic kicks in (see https://github.com/puppeteer/puppeteer/issues/2427).
+    return {
+      page: window.__coverage__ ? JSON.stringify(window.__coverage__) : null,
+      worker: workerCoverage ? JSON.stringify(workerCoverage) : null,
+    };
   });
+
+  if (coverage.page) {
+    mergeCoverageIntoGlobal(JSON.parse(coverage.page));
+  }
+  if (coverage.worker) {
+    mergeCoverageIntoGlobal(JSON.parse(coverage.worker));
+  }
+
   await page.close({ runBeforeUnload: false });
 }
 
diff --git a/test/test.mjs b/test/test.mjs
index 62d813b34..fde169a81 100644
--- a/test/test.mjs
+++ b/test/test.mjs
@@ -890,6 +890,7 @@ async function startIntegrationTest() {
   sessions[0].numRuns = results.runs;
   sessions[0].numErrors = results.failures;
   sessions[0].failures = results.failureList;
+  sessions[0].coverage = globalThis.__coverage__;
   await Promise.all(sessions.map(session => closeSession(session.name)));
 }
 
diff --git a/test/unit/jasmine-boot.js b/test/unit/jasmine-boot.js
index 6c10293ee..6ffb29784 100644
--- a/test/unit/jasmine-boot.js
+++ b/test/unit/jasmine-boot.js
@@ -42,7 +42,7 @@
 
 import { GlobalWorkerOptions } from "pdfjs/display/worker_options.js";
 import { isNodeJS } from "../../src/shared/util.js";
-import { mergeWorkerCoverageIntoWindow } from "../coverage_utils.js";
+import { mergeCoverageIntoGlobal } from "../coverage_utils.js";
 import { MessageHandler } from "pdfjs/shared/message_handler.js";
 import { PDFWorker } from "pdfjs/display/api.js";
 import { TestReporter } from "../reporter.js";
@@ -156,7 +156,7 @@ function installWorkerCoverageHook() {
     const handler = new MessageHandler("main", "worker", webWorker);
     const promise = handler
       .sendWithPromise("GetWorkerCoverage", null)
-      .then(mergeWorkerCoverageIntoWindow)
+      .then(mergeCoverageIntoGlobal)
       .catch(e => {
         console.warn(`Failed to collect worker coverage: ${e}`);
       })