diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index dee22c4..2d75d8c 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -35,7 +35,7 @@ jobs:
           git clone -q --filter=blob:none --sparse --depth 1 --branch "jdk-${release%+*}-ga" https://github.com/openjdk/jdk25u.git build/ref/jdk25u
           dirs=$(grep -v '^#' test/jtreg/passing.txt | cut -d/ -f1-2 | sort -u | sed 's|^|test/jdk/|')
           git -C build/ref/jdk25u sparse-checkout set test/lib test/jdk/lib test/jdk/tools/lib $dirs
-          node scripts/jtreg/run.ts build/ref/jdk25u --only-passing --jobs 4
+          node scripts/jtreg/run.ts build/ref/jdk25u --only-passing --jobs 4 --timeout 600
       - run: pnpm build
       - name: Node entry on the built dist/
         run: node --expose-gc --test test/image.test.ts
diff --git a/package.json b/package.json
index 51d5692..0a04fd3 100644
--- a/package.json
+++ b/package.json
@@ -39,6 +39,9 @@
     "dist/jdk/jdk.localedata.txt",
     "dist/jdk/legal/"
   ],
+  "publishConfig": {
+    "access": "public"
+  },
   "engines": {
     "node": ">=23.6"
   },
diff --git a/src/fs.ts b/src/fs.ts
index 8d14aae..5d1fc19 100644
--- a/src/fs.ts
+++ b/src/fs.ts
@@ -27,6 +27,10 @@ export interface Backend {
   setMtime?(path: string, ms: number): boolean;
   // whether the host refuses to write the file, or to create it when it is missing
   denied?(path: string): boolean;
+  // sets the permission bits to f(current bits)
+  chmod?(path: string, f: (mode: number) => number): boolean;
+  // whether the host allows reading (4) and executing (1), as access(2)
+  access?(path: string, mode: number): boolean;
 }
 
 export function normalize(path: string): string {
@@ -165,6 +169,23 @@ export class VFS {
     const r = this.resolve(path);
     return !!r && r[0].writable && !!r[0].denied?.(r[1]);
   }
+
+  // undefined when the backend has no permission bits
+  chmod(path: string, f: (mode: number) => number): boolean | undefined {
+    if (DEVICES.has(normalize(path))) return false;
+    const r = this.resolve(path);
+    if (!r || !r[0].chmod) return undefined;
+    return r[0].writable && r[0].chmod(r[1], f);
+  }
+
+  // access(2) on an existing path: mode is 4 read, 2 write, 1 execute
+  access(path: string, mode: number): boolean {
+    if (DEVICES.has(normalize(path))) return true;
+    const r = this.resolve(path);
+    if (!r) return false;
+    if (mode & 2 && (!r[0].writable || r[0].denied?.(r[1]))) return false;
+    return !(mode & 5) || (r[0].access?.(r[1], mode & 5) ?? true);
+  }
 }
 
 // Writable in-memory tree, for /tmp, /files and strings added by the page.
diff --git a/src/natives/io.ts b/src/natives/io.ts
index 660c5cd..bb978c8 100644
--- a/src/natives/io.ts
+++ b/src/natives/io.ts
@@ -192,8 +192,15 @@ export function fileOf(t: JThread, fd: number): OpenFile {
 
 export function flush(t: JThread, f: OpenFile) {
   if (f.dirty && f.writable && f.path) {
-    t.vm.fs.write(f.path, f.data.slice(0, f.size));
-    f.dirty = false;
+    const data = f.data.slice(0, f.size);
+    let ok = t.vm.fs.write(f.path, data);
+    // an open file keeps its write access when the file's mode changes, as an fd does
+    let mode = 0;
+    if (!ok && t.vm.fs.chmod(f.path, (m) => (mode = m) | 0o200)) {
+      ok = t.vm.fs.write(f.path, data);
+      t.vm.fs.chmod(f.path, () => mode);
+    }
+    if (ok) f.dirty = false;
   }
 }
 
@@ -278,6 +285,11 @@ function attrs(t: JThread, file: JObject): number {
   return 1 | (st.dir ? 4 : st.device ? 0 : 2);
 }
 
+// a backend without permission bits takes any change to an existing file
+function chmod(t: JThread, file: JObject, f: (mode: number) => number): boolean {
+  return t.vm.fs.chmod(resolvePath(t, pathOf(t, file)), f) ?? attrs(t, file) !== 0;
+}
+
 function pathOf(t: JThread, file: JObject): string {
   return t.vm.jsString(t.vm.getField(file, "java/io/File", "path"));
 }
@@ -375,8 +387,7 @@ export const natives: Natives = {
   [`${UFS}.getBooleanAttributes0(Ljava/io/File;)I`]: (t, [, f]) => attrs(t, f),
   [`${UFS}.checkAccess0(Ljava/io/File;I)Z`]: (t, [, f, access]) => {
     const abs = resolvePath(t, pathOf(t, f));
-    if (!t.vm.fs.stat(abs)) return 0;
-    return (access & 2) === 0 || (t.vm.fs.writable(abs) && !t.vm.fs.denied(abs));
+    return !!t.vm.fs.stat(abs) && t.vm.fs.access(abs, access);
   },
   [`${UFS}.getLastModifiedTime0(Ljava/io/File;)J`]: (t, [, f]) => BigInt(Math.floor(t.vm.fs.stat(resolvePath(t, pathOf(t, f)))?.mtime ?? 0)),
   [`${UFS}.getLength0(Ljava/io/File;)J`]: (t, [, f]) => {
@@ -384,7 +395,10 @@ export const natives: Natives = {
     syncPath(t, abs);
     return BigInt(t.vm.fs.stat(abs)?.size ?? 0);
   },
-  [`${UFS}.setPermission0(Ljava/io/File;IZZ)Z`]: (t, [, f]) => attrs(t, f) !== 0,
+  [`${UFS}.setPermission0(Ljava/io/File;IZZ)Z`]: (t, [, f, access, enable, ownerOnly]) => {
+    const bits = ownerOnly ? access << 6 : access * 0o111;
+    return chmod(t, f, (m) => (enable ? m | bits : m & ~bits));
+  },
   [`${UFS}.createFileExclusively0(Ljava/lang/String;)Z`]: (t, [, p]) => {
     const abs = resolvePath(t, t.vm.jsString(p));
     if (t.vm.fs.stat(abs)) return 0;
@@ -401,7 +415,7 @@ export const natives: Natives = {
   [`${UFS}.rename0(Ljava/io/File;Ljava/io/File;)Z`]: (t, [, a, b]) =>
     renamePath(t, resolvePath(t, pathOf(t, a)), resolvePath(t, pathOf(t, b))),
   [`${UFS}.setLastModifiedTime0(Ljava/io/File;J)Z`]: (t, [, f, ms]) => setMtime(t, resolvePath(t, pathOf(t, f)), Number(ms)),
-  [`${UFS}.setReadOnly0(Ljava/io/File;)Z`]: (t, [, f]) => attrs(t, f) !== 0,
+  [`${UFS}.setReadOnly0(Ljava/io/File;)Z`]: (t, [, f]) => chmod(t, f, (m) => m & ~0o222),
   [`${UFS}.getSpace0(Ljava/io/File;I)J`]: () => 0n,
   [`${UFS}.getNameMax0(Ljava/lang/String;)J`]: () => 255n,
 };
diff --git a/src/natives/nio.ts b/src/natives/nio.ts
index 8b6eb78..091a0b4 100644
--- a/src/natives/nio.ts
+++ b/src/natives/nio.ts
@@ -113,7 +113,7 @@ export const natives: Natives = {
   [`${N}access0(JI)I`]: (t, [p, amode]) => {
     const abs = path(t, p);
     if (!t.vm.fs.stat(abs)) return ENOENT;
-    return amode & 2 && (!t.vm.fs.writable(abs) || t.vm.fs.denied(abs)) ? EACCES : 0;
+    return t.vm.fs.access(abs, amode) ? 0 : EACCES;
   },
   [`${N}open0(JII)I`]: (t, [p, flags]) => {
     const abs = path(t, p);
diff --git a/src/node.ts b/src/node.ts
index 8105894..71f9c31 100644
--- a/src/node.ts
+++ b/src/node.ts
@@ -81,6 +81,22 @@ export class NodeBackend implements Backend {
       return (e as NodeJS.ErrnoException).code === "EACCES" || (e as NodeJS.ErrnoException).code === "EPERM";
     }
   }
+  chmod(p: string, f: (mode: number) => number) {
+    try {
+      fs.chmodSync(this.host(p), f(fs.statSync(this.host(p)).mode & 0o7777));
+      return true;
+    } catch {
+      return false;
+    }
+  }
+  access(p: string, mode: number) {
+    try {
+      fs.accessSync(this.host(p), mode);
+      return true;
+    } catch {
+      return false;
+    }
+  }
   setMtime(p: string, ms: number) {
     try {
       fs.utimesSync(this.host(p), fs.statSync(this.host(p)).atime, ms / 1000);
diff --git a/test/permissions/Permissions.java b/test/permissions/Permissions.java
index 196de0e..a0ddd0c 100644
--- a/test/permissions/Permissions.java
+++ b/test/permissions/Permissions.java
@@ -4,7 +4,8 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 
-// Writes the host refuses: args are a read-only file and a read-only directory.
+// Writes the host refuses: args are a read-only file, a read-only directory and a
+// writable file.
 public class Permissions {
   public static void main(String[] args) throws Exception {
     Path file = Path.of(args[0]), dir = Path.of(args[1]);
@@ -30,5 +31,17 @@ public static void main(String[] args) throws Exception {
       System.out.println(e.getClass().getName());
     }
     System.out.println(Files.isWritable(dir) + " " + Files.exists(dir.resolve("new.txt")));
+    File w = new File(args[2]);
+    System.out.println(w.setReadOnly() + " " + w.canWrite());
+    System.out.println(w.setWritable(true) + " " + w.canWrite());
+    System.out.println(w.canExecute() + " " + w.setExecutable(true) + " " + w.canExecute());
+    try (var out = new FileOutputStream(w)) {
+      out.write('a');
+      w.setReadOnly();
+      out.write('b');
+    }
+    w.setWritable(true);
+    System.out.println(Files.readString(w.toPath()));
+    System.out.println(w.setReadable(false) + " " + w.canRead() + " " + Files.isReadable(w.toPath()));
   }
 }
diff --git a/test/programs.test.ts b/test/programs.test.ts
index 3a71054..448e6cc 100644
--- a/test/programs.test.ts
+++ b/test/programs.test.ts
@@ -122,14 +122,17 @@ test("permission denied", { skip: process.getuid?.() === 0 }, async () => {
   const classes = join(root, "build", "test-permissions");
   execFileSync(hotspot("javac"), ["-d", classes, join(root, "test", "permissions", "Permissions.java")]);
   const dir = mkdtempSync(join(tmpdir(), "java-web-perm-"));
-  const file = join(dir, "read-only.txt"), locked = join(dir, "locked");
+  const file = join(dir, "read-only.txt"), locked = join(dir, "locked"), open = join(dir, "open.txt");
   writeFileSync(file, "x");
   chmodSync(file, 0o444);
   mkdirSync(locked, { mode: 0o555 });
   try {
-    const ref = spawnSync(hotspot("java"), ["-cp", classes, "Permissions", file, locked], { encoding: "utf8" });
+    writeFileSync(open, "x");
+    const ref = spawnSync(hotspot("java"), ["-cp", classes, "Permissions", file, locked, open], { encoding: "utf8" });
+    writeFileSync(open, "x");
+    chmodSync(open, 0o644);
     const stdout: Uint8Array[] = [];
-    const code = await runNode({ classpath: [classes], mainClass: "Permissions", args: [file, locked], stdout: (b) => stdout.push(b) });
+    const code = await runNode({ classpath: [classes], mainClass: "Permissions", args: [file, locked, open], stdout: (b) => stdout.push(b) });
     assert.equal(Buffer.concat(stdout).toString("utf8"), ref.stdout);
     assert.equal(code, ref.status);
   } finally {