diff --git a/src/bundler/defines.rs b/src/bundler/defines.rs
index 8897c2649eb2..fb0ae068822c 100644
--- a/src/bundler/defines.rs
+++ b/src/bundler/defines.rs
@@ -51,12 +51,8 @@ fn env_string_store_put(
     key: &[u8],
     value: &[u8],
 ) -> Result<(), crate::Error> {
-    // The `E.String` slab must NOT live in the thread-local
-    // `Expr.Data.Store` — `configureDefines` resets that store on return, so
-    // the env-define payloads must outlive it. Allocate from `bump` (the
-    // transpiler arena) so the slab is bulk-freed with the `Define` table
-    // instead of leaking a `Box` per env var. Value bytes alias the long-lived
-    // env-map storage.
+    // Copied because `Bun__setEnvValue` frees the env-map entry `value` points into.
+    let value: &[u8] = bump.alloc_slice_copy(value);
     let value: ExprData = ExprData::EString(bun_ast::StoreRef::from_bump(
         bump.alloc(bun_ast::E::EString::init(value)),
     ));
diff --git a/src/dotenv/env_loader.rs b/src/dotenv/env_loader.rs
index 57b4464602a8..ab2858f0663f 100644
--- a/src/dotenv/env_loader.rs
+++ b/src/dotenv/env_loader.rs
@@ -336,6 +336,7 @@ impl Loader {
     /// Get proxy URL for HTTP/HTTPS requests, respecting NO_PROXY.
     /// `hostname` is the host without port (e.g., "localhost")
     /// `host` is the host with port if present (e.g., "localhost:3000")
+    /// The returned URL borrows the map entry, which `Map::put` frees.
     pub fn get_http_proxy(
         &self,
         is_http: bool,
@@ -1394,6 +1395,7 @@ impl Map {
         }
     }
 
+    /// Frees the old value; JS hits this via `Bun__setEnvValue`, so don't hold borrows across JS.
     #[inline]
     pub fn put(&mut self, key: &[u8], value: &[u8]) -> Result<(), AllocError> {
         #[cfg(all(windows, debug_assertions))]
diff --git a/src/jsc/rare_data.rs b/src/jsc/rare_data.rs
index 8476ef60cb1b..8ca9cbf26261 100644
--- a/src/jsc/rare_data.rs
+++ b/src/jsc/rare_data.rs
@@ -537,8 +537,7 @@ impl ProxyEnvSlots {
 // RefCountedEnvValue
 // ──────────────────────────────────────────────────────────────────────────
 
-/// A ref-counted heap-allocated byte slice. The env map stores borrowed
-/// `.bytes` slices; as long as any VM holds a ref, the bytes stay valid.
+/// Last JS-assigned proxy value, shared with later Workers; the env map keeps its own copy.
 ///
 /// Holders are `Arc<RefCountedEnvValue>` (per LIFETIMES.tsv): the refcount
 /// lives in the `Arc` header, so ref/deref are `Arc::clone`/`drop`.
diff --git a/test/bake/dev/bundle.test.ts b/test/bake/dev/bundle.test.ts
index 6c6d3657029c..8832a384ab79 100644
--- a/test/bake/dev/bundle.test.ts
+++ b/test/bake/dev/bundle.test.ts
@@ -1,6 +1,6 @@
 // Bundle tests are tests concerning bundling bugs that only occur in DevServer.
 import { expect } from "bun:test";
-import { devTest, emptyHtmlFile, minimalFramework } from "../bake-harness";
+import { Dev, devTest, emptyHtmlFile, minimalFramework } from "../bake-harness";
 
 devTest("import identifier doesnt get renamed", {
   framework: minimalFramework,
@@ -865,3 +865,57 @@ devTest("barrel optimization: namespace re-export cycle through a star-exported
     await c.expectMessage("result: object Y KEEP DEEP OTHER");
   },
 });
+
+// With `[serve.static] env = "inline"`, DevServer builds its define table from
+// the VM's env map once at startup and keeps it for the life of the server.
+// Assigning a proxy variable on process.env replaces that variable's entry in
+// the env map, so the define must own a copy of the value instead of pointing
+// into the map; otherwise every rebuild of a module that reads the variable
+// inlines freed memory.
+const startupProxy = "http://proxy-at-startup.example:8080/" + Buffer.alloc(120, "a").toString();
+async function clientBundle(dev: Dev) {
+  const html = await dev.fetch("/").text();
+  const scripts = [...html.matchAll(/src="([^"]+\.js)"/g)];
+  expect(scripts).toHaveLength(1);
+  return dev.fetch(scripts[0][1]).text();
+}
+devTest("inlined env var survives a runtime process.env write to a proxy variable", {
+  files: {
+    "bunfig.toml": `
+      [serve.static]
+      env = "inline"
+    `,
+    "index.html": emptyHtmlFile({ scripts: ["index.ts"] }),
+    "index.ts": `console.log("v1", process.env.HTTPS_PROXY);`,
+    "bun.app.ts": `
+      import html from "./index.html";
+      export default {
+        static: { "/": html },
+        fetch(req) {
+          if (new URL(req.url).pathname === "/set-proxy") {
+            process.env.HTTPS_PROXY = "http://changed-at-runtime.example:1/";
+            return new Response("ok");
+          }
+          return new Response("Not Found", { status: 404 });
+        },
+      };
+    `,
+  },
+  htmlFiles: [],
+  env: { HTTPS_PROXY: startupProxy },
+  async test(dev) {
+    const before = await clientBundle(dev);
+    expect(before).toContain('"v1"');
+    expect(before).toContain(startupProxy);
+
+    await dev.fetch("/set-proxy").equals("ok");
+
+    // Rebuilding index.ts prints the define again, now that the env map entry
+    // it was created from is gone.
+    await dev.write("index.ts", `console.log("v2", process.env.HTTPS_PROXY);`);
+    const after = await clientBundle(dev);
+    expect(after).toContain('"v2"');
+    expect(after).toContain(startupProxy);
+    expect(after).not.toContain("changed-at-runtime");
+  },
+});
diff --git a/test/bundler/bundler_env.test.ts b/test/bundler/bundler_env.test.ts
index b87ab47ab605..1f33d41316b3 100644
--- a/test/bundler/bundler_env.test.ts
+++ b/test/bundler/bundler_env.test.ts
@@ -1,4 +1,5 @@
-import { describe } from "bun:test";
+import { describe, expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDir } from "harness";
 import { itBundled } from "./expectBundled";
 
 for (let backend of ["api", "cli"] as const) {
@@ -118,3 +119,78 @@ for (let backend of ["api", "cli"] as const) {
       });
   });
 }
+
+// The define table is built from the env map when the build is configured.
+// Assigning one of the proxy variables on process.env (the only process.env
+// writes that reach the native env map) replaces the map entry that define was
+// built from, so the define has to own its value: here that write happens
+// while the build is still running, from a macro and from a plugin.
+const proxyAtStart = "http://proxy-at-start.example:8080/" + Buffer.alloc(120, "a").toString();
+
+describe("bundler/cli", () => {
+  itBundled("env/inline survives macro proxy write", {
+    backend: "cli",
+    dotenv: "inline",
+    env: { HTTPS_PROXY: proxyAtStart },
+    files: {
+      "/a.ts": /* ts */ `
+        import { setProxy } from "./macro.ts" with { type: "macro" };
+        setProxy();
+        console.log(process.env.HTTPS_PROXY);
+      `,
+      "/macro.ts": /* ts */ `
+        export function setProxy() {
+          process.env.HTTPS_PROXY = "http://changed-by-macro.example:1/";
+          return 0;
+        }
+      `,
+    },
+    onAfterBundle(api) {
+      api.expectFile("/out.js").toContain(proxyAtStart);
+      api.expectFile("/out.js").not.toContain("changed-by-macro");
+    },
+    run: {
+      env: { HTTPS_PROXY: "http://not-inlined.example:1/" },
+      stdout: proxyAtStart + "\n",
+    },
+  });
+});
+
+describe("bundler/api", () => {
+  test.concurrent("env: inline survives a plugin assigning a proxy variable during the build", async () => {
+    using dir = tempDir("bundler-env-inline-plugin-proxy", {
+      "entry.ts": `export const replaced = "by the plugin";`,
+      "build.ts": /* ts */ `
+        const result = await Bun.build({
+          entrypoints: ["./entry.ts"],
+          env: "inline",
+          plugins: [{
+            name: "assign-proxy",
+            setup(build) {
+              build.onLoad({ filter: /entry\\.ts$/ }, () => {
+                process.env.HTTPS_PROXY = "http://changed-by-plugin.example:1/";
+                return { loader: "ts", contents: "export const proxy = process.env.HTTPS_PROXY;" };
+              });
+            },
+          }],
+        });
+        if (!result.success) throw new AggregateError(result.logs, "build failed");
+        process.stdout.write(await result.outputs[0].text());
+      `,
+    });
+
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "build.ts"],
+      cwd: String(dir),
+      env: { ...bunEnv, HTTPS_PROXY: proxyAtStart },
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+    expect(stdout).toContain(`var proxy = ${JSON.stringify(proxyAtStart)};`);
+    expect(stdout).not.toContain("changed-by-plugin");
+    expect(stderr).toBe("");
+    expect(exitCode).toBe(0);
+  });
+});
diff --git a/test/js/web/workers/worker.test.ts b/test/js/web/workers/worker.test.ts
index 49e7a197ed19..cff37fbe1bac 100644
--- a/test/js/web/workers/worker.test.ts
+++ b/test/js/web/workers/worker.test.ts
@@ -168,6 +168,44 @@ describe("web worker", () => {
     expect(exitCode).toBe(0);
   });
 
+  // A worker's transpiler builds its process.env defines from the worker's env
+  // map when the worker starts. Assigning a proxy variable replaces that map
+  // entry, so a module transpiled afterwards must not read the old entry's
+  // memory. Spawned so the launch value is set without touching this
+  // process's proxy settings.
+  test("worker-env: a module transpiled after the worker assigns HTTPS_PROXY sees a real value", async () => {
+    const launchValue = "http://proxy-at-launch.example:8080/" + Buffer.alloc(120, "a").toString();
+    const workerValue = "http://assigned-in-worker.example:1/" + Buffer.alloc(120, "b").toString();
+    using dir = tempDir("worker-env-proxy-define", {
+      "main.ts": `
+        const worker = new Worker(new URL("./worker.ts", import.meta.url).href);
+        worker.onerror = e => { console.error(e.message); process.exit(1); };
+        worker.onmessage = e => {
+          console.log(JSON.stringify(e.data));
+          worker.terminate();
+        };
+      `,
+      "worker.ts": `
+        process.env.HTTPS_PROXY = ${JSON.stringify(workerValue)};
+        const { proxy } = await import("./mod.ts");
+        postMessage(proxy);
+      `,
+      "mod.ts": `export const proxy = process.env.HTTPS_PROXY;`,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "main.ts"],
+      cwd: String(dir),
+      env: { ...bunEnv, HTTPS_PROXY: launchValue },
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toBe("");
+    // Either value is a correct answer (it depends on whether worker
+    // transpiles inline process.env reads); bytes of a freed map entry are not.
+    expect(JSON.parse(stdout)).toBeOneOf([launchValue, workerValue]);
+    expect(exitCode).toBe(0);
+  });
+
   test("worker-env with a lot of properties", done => {
     const obj: any = {};