diff --git a/core/audits/byte-efficiency/render-blocking-resources.js b/core/audits/byte-efficiency/render-blocking-resources.js
index c5e8d94eddee..fea0d923327a 100644
--- a/core/audits/byte-efficiency/render-blocking-resources.js
+++ b/core/audits/byte-efficiency/render-blocking-resources.js
@@ -38,10 +38,10 @@ const str_ = i18n.createIcuMessageFn(import.meta.url, UIStrings);
 /**
  * Given a simulation's nodeTimings, return an object with the nodes/timing keyed by network URL
  * @param {LH.Gatherer.Simulation.Result['nodeTimings']} nodeTimings
- * @return {Map<string, {node: LH.Gatherer.Simulation.GraphNode, nodeTiming: LH.Gatherer.Simulation.NodeTiming}>}
+ * @return {Map<string, {node: LH.Gatherer.Simulation.GraphNetworkNode, nodeTiming: LH.Gatherer.Simulation.NodeTiming}>}
  */
 function getNodesAndTimingByRequestId(nodeTimings) {
-  /** @type {Map<string, {node: LH.Gatherer.Simulation.GraphNode, nodeTiming: LH.Gatherer.Simulation.NodeTiming}>} */
+  /** @type {Map<string, {node: LH.Gatherer.Simulation.GraphNetworkNode, nodeTiming: LH.Gatherer.Simulation.NodeTiming}>} */
   const requestIdToNode = new Map();
 
   for (const [node, nodeTiming] of nodeTimings) {
@@ -169,7 +169,7 @@ class RenderBlockingResources extends Audit {
 
       results.push({
         url: resource.args.data.url,
-        totalBytes: resource.args.data.encodedDataLength,
+        totalBytes: node.request.transferSize,
         wastedMs,
       });
     }
diff --git a/core/test/audits/byte-efficiency/render-blocking-resources-test.js b/core/test/audits/byte-efficiency/render-blocking-resources-test.js
index e952c6f89e76..8c44d2398c7f 100644
--- a/core/test/audits/byte-efficiency/render-blocking-resources-test.js
+++ b/core/test/audits/byte-efficiency/render-blocking-resources-test.js
@@ -17,6 +17,8 @@ const {Simulator} = Lantern.Simulation;
 
 const trace = readJson('../../fixtures/artifacts/render-blocking/trace.json', import.meta);
 const devtoolsLog = readJson('../../fixtures/artifacts/render-blocking/devtoolslog.json', import.meta);
+const lrTrace = readJson('../../fixtures/artifacts/lr/trace.json.gz', import.meta);
+const lrDevtoolsLog = readJson('../../fixtures/artifacts/lr/devtoolslog.json.gz', import.meta);
 
 const mobileSlow4G = constants.throttling.mobileSlow4G;
 
@@ -38,6 +40,47 @@ describe('Render blocking resources audit', () => {
     assert.deepStrictEqual(result.metricSavings, {FCP: 300, LCP: 0});
   });
 
+  describe('Lightrider', () => {
+    before(() => {
+      global.isLightrider = true;
+    });
+
+    after(() => {
+      global.isLightrider = undefined;
+    });
+
+    it('considers X-TotalFetchedSize in its reported transfer size', async () => {
+      // TODO(15841): The trace backend knows nothing of Lantern.
+      if (process.env.INTERNAL_LANTERN_USE_TRACE !== undefined) {
+        return;
+      }
+
+      const artifacts = {
+        URL: getURLArtifactFromDevtoolsLog(lrDevtoolsLog),
+        GatherContext: {gatherMode: 'navigation'},
+        traces: {defaultPass: lrTrace},
+        devtoolsLogs: {defaultPass: lrDevtoolsLog},
+        Stacks: [],
+      };
+
+      const settings = {throttlingMethod: 'simulate', throttling: mobileSlow4G};
+      const computedCache = new Map();
+      const result = await RenderBlockingResourcesAudit.audit(artifacts, {settings, computedCache});
+      expect(result.details.items).toMatchInlineSnapshot(`
+  Array [
+    Object {
+      "totalBytes": 128188,
+      "url": "https://www.llentab.cz/wp-content/uploads/fusion-styles/715df3f482419a9ed822189df6e57839.min.css?ver=3.11.10",
+      "wastedMs": 750,
+    },
+  ]
+  `);
+      assert.equal(result.score, 0);
+      assert.equal(result.numericValue, 0);
+      assert.deepStrictEqual(result.metricSavings, {FCP: 0, LCP: 0});
+    });
+  });
+
   it('evaluates correct wastedMs when LCP is text', async () => {
     const textLcpTrace = JSON.parse(JSON.stringify(trace));
 
diff --git a/core/test/fixtures/artifacts/lr/devtoolslog.json.gz b/core/test/fixtures/artifacts/lr/devtoolslog.json.gz
new file mode 100644
index 000000000000..03ce7efb4384
Binary files /dev/null and b/core/test/fixtures/artifacts/lr/devtoolslog.json.gz differ
diff --git a/core/test/fixtures/artifacts/lr/trace.json.gz b/core/test/fixtures/artifacts/lr/trace.json.gz
new file mode 100644
index 000000000000..adf41e76679b
Binary files /dev/null and b/core/test/fixtures/artifacts/lr/trace.json.gz differ
diff --git a/core/test/results/sample_v2.json b/core/test/results/sample_v2.json
index 3bb96b2184bd..4100e87395e7 100644
--- a/core/test/results/sample_v2.json
+++ b/core/test/results/sample_v2.json
@@ -4496,7 +4496,7 @@
           },
           {
             "url": "http://localhost:10200/dobetterweb/unknown404.css?delay=200",
-            "totalBytes": 0,
+            "totalBytes": 235,
             "wastedMs": 881
           },
           {
@@ -4516,7 +4516,7 @@
           },
           {
             "url": "http://localhost:10200/dobetterweb/fcp-delayer.js?delay=5000",
-            "totalBytes": 0,
+            "totalBytes": 249,
             "wastedMs": 881
           }
         ],