diff --git a/src/instrumentation/libraries/http/Instrumentation.ts b/src/instrumentation/libraries/http/Instrumentation.ts
index 2478430b..2d602845 100644
--- a/src/instrumentation/libraries/http/Instrumentation.ts
+++ b/src/instrumentation/libraries/http/Instrumentation.ts
@@ -413,7 +413,8 @@ export class HttpInstrumentation extends TdInstrumentationBase {
       const statusCode = res.statusCode;
 
       // Capture any final response data
-      if (chunk) {
+      // res.end(callback) passes the callback as the first argument; it is not body data
+      if (chunk && typeof chunk !== "function") {
         responseChunks.push(chunk);
       }
 
@@ -755,7 +756,8 @@ export class HttpInstrumentation extends TdInstrumentationBase {
     if (originalEnd) {
       req.end = function (chunk?: any, encoding?: any, callback?: any): ClientRequest {
         // Capture final chunk if provided
-        if (chunk && !requestBodyCaptured) {
+        // req.end(callback) passes the callback as the first argument; it is not body data
+        if (chunk && typeof chunk !== "function" && !requestBodyCaptured) {
           requestBodyChunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk, encoding));
         }
 
diff --git a/src/instrumentation/libraries/http/integration-tests/end-callback.test.ts b/src/instrumentation/libraries/http/integration-tests/end-callback.test.ts
new file mode 100644
index 00000000..f743e0ba
--- /dev/null
+++ b/src/instrumentation/libraries/http/integration-tests/end-callback.test.ts
@@ -0,0 +1,176 @@
+process.env.TUSK_DRIFT_MODE = "RECORD";
+
+import { TuskDrift } from "../../../../core/TuskDrift";
+
+TuskDrift.initialize({
+  apiKey: "test-api-key-end-callback",
+  env: "test",
+  logLevel: "silent",
+});
+TuskDrift.markAppAsReady();
+
+import { SpanKind } from "@opentelemetry/api";
+import {
+  InMemorySpanAdapter,
+  registerInMemoryAdapter,
+  clearRegisteredInMemoryAdapters,
+} from "../../../../core/tracing/adapters/InMemorySpanAdapter";
+import { waitForSpans } from "./test-utils";
+import test from "ava";
+import type { Server, RequestOptions } from "http";
+import { AddressInfo } from "net";
+
+const spanAdapter = new InMemorySpanAdapter();
+registerInMemoryAdapter(spanAdapter);
+
+// Require http after TuskDrift.initialize() so the require-in-the-middle hook patches it,
+// matching how the SDK is used in an application.
+const http: typeof import("http") = require("http");
+
+let server: Server;
+let port: number;
+
+function decodeBody(value: unknown): string {
+  return Buffer.from(String(value), "base64").toString("utf8");
+}
+
+function makeRequest(
+  options: RequestOptions,
+  body?: string,
+  endWithCallback = false,
+): Promise<{ statusCode: number; data: string }> {
+  return new Promise((resolve, reject) => {
+    const req = http.request(options, (res) => {
+      let data = "";
+      res.on("data", (chunk) => (data += chunk));
+      res.on("end", () => resolve({ statusCode: res.statusCode || 0, data }));
+    });
+    req.on("error", reject);
+    if (body) {
+      req.write(body);
+    }
+    if (endWithCallback) {
+      // Node's documented signature: request.end([data[, encoding]][, callback])
+      req.end(() => {});
+    } else {
+      req.end();
+    }
+  });
+}
+
+test.before(async () => {
+  server = http.createServer((req, res) => {
+    if (req.url === "/upstream") {
+      let body = "";
+      req.on("data", (chunk) => (body += chunk));
+      req.on("end", () => {
+        res.setHeader("content-type", "application/json");
+        res.end(JSON.stringify({ upstreamReceived: body }));
+      });
+      return;
+    }
+
+    if (req.url === "/call-upstream") {
+      // Outbound request made inside the inbound span, ended with a callback-only end().
+      const postData = JSON.stringify({ hello: "world" });
+      try {
+        makeRequest(
+          {
+            hostname: "127.0.0.1",
+            port,
+            path: "/upstream",
+            method: "POST",
+            headers: {
+              "content-type": "application/json",
+              "content-length": Buffer.byteLength(postData),
+            },
+          },
+          postData,
+          true,
+        ).then(
+          (upstream) => {
+            res.setHeader("content-type", "application/json");
+            res.end(JSON.stringify({ upstream: JSON.parse(upstream.data) }));
+          },
+          (error: Error) => {
+            res.statusCode = 500;
+            res.setHeader("content-type", "application/json");
+            res.end(JSON.stringify({ error: error.message }));
+          },
+        );
+      } catch (error) {
+        res.statusCode = 500;
+        res.setHeader("content-type", "application/json");
+        res.end(JSON.stringify({ error: (error as Error).message }));
+      }
+      return;
+    }
+
+    // Inbound handler that writes the body, then ends with a callback-only end().
+    res.setHeader("content-type", "application/json");
+    res.write(JSON.stringify({ path: req.url }));
+    res.end(() => {});
+  });
+
+  await new Promise<void>((resolve) => server.listen(0, "127.0.0.1", resolve));
+  port = (server.address() as AddressInfo).port;
+});
+
+test.after.always(async () => {
+  await new Promise<void>((resolve, reject) =>
+    server.close((err?: Error) => (err ? reject(err) : resolve())),
+  );
+  clearRegisteredInMemoryAdapters();
+});
+
+test("inbound: response body is recorded when the handler calls res.end(callback)", async (t) => {
+  const response = await makeRequest({
+    hostname: "127.0.0.1",
+    port,
+    path: "/inbound",
+    method: "GET",
+  });
+
+  t.is(response.statusCode, 200);
+  t.deepEqual(JSON.parse(response.data), { path: "/inbound" });
+
+  await waitForSpans();
+
+  const serverSpan = spanAdapter
+    .getAllSpans()
+    .find(
+      (span) => span.kind === SpanKind.SERVER && (span.inputValue as any)?.target === "/inbound",
+    );
+  t.truthy(serverSpan, "Expected a SERVER span for /inbound");
+
+  const outputValue = serverSpan!.outputValue as any;
+  t.truthy(outputValue.body, "Expected the recorded server span to carry the response body");
+  t.deepEqual(JSON.parse(decodeBody(outputValue.body)), { path: "/inbound" });
+});
+
+test("outbound: req.end(callback) inside a trace does not throw and the request body is recorded", async (t) => {
+  const response = await makeRequest({
+    hostname: "127.0.0.1",
+    port,
+    path: "/call-upstream",
+    method: "GET",
+  });
+
+  t.is(response.statusCode, 200, `Unexpected response: ${response.data}`);
+  t.deepEqual(JSON.parse(response.data), {
+    upstream: { upstreamReceived: JSON.stringify({ hello: "world" }) },
+  });
+
+  await waitForSpans();
+
+  const clientSpan = spanAdapter
+    .getAllSpans()
+    .find(
+      (span) => span.kind === SpanKind.CLIENT && (span.inputValue as any)?.path === "/upstream",
+    );
+  t.truthy(clientSpan, "Expected a CLIENT span for /upstream");
+
+  const inputValue = clientSpan!.inputValue as any;
+  t.truthy(inputValue.body, "Expected the recorded client span to carry the request body");
+  t.deepEqual(JSON.parse(decodeBody(inputValue.body)), { hello: "world" });
+});
diff --git a/src/instrumentation/libraries/nextjs/Instrumentation.ts b/src/instrumentation/libraries/nextjs/Instrumentation.ts
index 23202a4f..760a659c 100644
--- a/src/instrumentation/libraries/nextjs/Instrumentation.ts
+++ b/src/instrumentation/libraries/nextjs/Instrumentation.ts
@@ -352,7 +352,8 @@ export class NextjsInstrumentation extends TdInstrumentationBase {
     const originalEnd = actualRes.end?.bind(actualRes);
     if (originalEnd) {
       actualRes.end = function (chunk?: any, encoding?: any, callback?: any) {
-        if (chunk) {
+        // res.end(callback) passes the callback as the first argument; it is not body data
+        if (chunk && typeof chunk !== "function") {
           responseChunks.push(chunk);
         }
         return originalEnd.call(this, chunk, encoding, callback);