diff --git a/src/bundler/bundle_v2.rs b/src/bundler/bundle_v2.rs
index 69a5625b1974..a5516174e964 100644
--- a/src/bundler/bundle_v2.rs
+++ b/src/bundler/bundle_v2.rs
@@ -4122,24 +4122,23 @@ pub mod bv2_impl {
                         let source = &mut sources[index];
 
                         let output_path: Box<[u8]> = {
-                            // TODO: outbase
-                            let pathname =
-                                Fs::PathName::init(bun_paths::resolve_path::relative_platform::<
-                                    bun_paths::resolve_path::platform::Loose,
-                                    false,
-                                >(
-                                    &self.transpiler.options.root_dir,
-                                    source.path.text,
-                                ));
+                            let pathname = Fs::PathName::init(source.path.text);
 
                             template.placeholder.name = pathname.base.to_vec().into_boxed_slice();
-                            template.placeholder.dir = pathname.dir.to_vec().into_boxed_slice();
                             let mut ext: &[u8] = pathname.ext;
                             if !ext.is_empty() && ext[0] == b'.' {
                                 ext = &ext[1..];
                             }
                             template.placeholder.ext = ext.to_vec().into_boxed_slice();
 
+                            if template.needs(options::PlaceholderField::Dir) {
+                                template.placeholder.dir = options::source_dir_relative_to_root(
+                                    pathname.dir,
+                                    &self.transpiler.options.root_dir,
+                                    source.path.is_file(),
+                                )?;
+                            }
+
                             if template.needs(options::PlaceholderField::Hash) {
                                 template.placeholder.hash =
                                     Some(content_hashes_for_additional_files[index]);
diff --git a/src/bundler/linker_context/computeChunks.rs b/src/bundler/linker_context/computeChunks.rs
index 07de93c10b1e..00d5a0191bb1 100644
--- a/src/bundler/linker_context/computeChunks.rs
+++ b/src/bundler/linker_context/computeChunks.rs
@@ -5,7 +5,6 @@ use core::sync::atomic::AtomicUsize;
 use bun_alloc::Arena; // bumpalo::Bump re-export
 use bun_collections::{ArrayHashMap, AutoBitSet, VecExt};
 use bun_core::strings;
-use bun_paths::{PathBuffer, resolve_path};
 use bun_sourcemap::SourceMapPieces;
 use bun_wyhash::{self, Wyhash};
 
@@ -634,46 +633,11 @@ pub fn compute_chunks(this: &mut LinkerContext, unique_key: u64) -> crate::Resul
         }
 
         if chunk.template.needs(PlaceholderField::Dir) {
-            // this if check is a specific fix for `bun build hi.ts --external '*'`, without leading `./`
-            let dir_path: &[u8] = if !pathname.dir.is_empty() {
-                pathname.dir
-            } else {
-                b"."
-            };
-            let mut real_path_buf = PathBuffer::uninit();
-            let dir: &[u8] = 'dir: {
-                let Ok(dir_file) = bun_sys::File::openat(
-                    bun_sys::Fd::cwd(),
-                    dir_path,
-                    bun_sys::O::PATH | bun_sys::O::DIRECTORY,
-                    0,
-                ) else {
-                    break 'dir &*resolve_path::normalize_buf::<bun_paths::platform::Auto>(
-                        dir_path,
-                        &mut real_path_buf.0,
-                    );
-                };
-
-                match dir_file.get_path(&mut real_path_buf) {
-                    Ok(p) => break 'dir p,
-                    Err(err) => {
-                        // Split-borrow — see `LinkerContext::log_disjoint`.
-                        this.log_disjoint().add_error_fmt(
-                            None,
-                            bun_ast::Loc::EMPTY,
-                            format_args!(
-                                "{}: Failed to get full path for directory '{}'",
-                                bstr::BStr::new(err.name()),
-                                bstr::BStr::new(dir_path)
-                            ),
-                        );
-                        return Err(crate::Error::BuildFailed);
-                    }
-                }
-            };
-
-            let root_dir = &this.resolver().opts.root_dir;
-            chunk.template.placeholder.dir = resolve_path::relative_alloc(root_dir, dir)?;
+            chunk.template.placeholder.dir = crate::options::source_dir_relative_to_root(
+                pathname.dir,
+                &this.resolver().opts.root_dir,
+                true,
+            )?;
         }
     }
 
diff --git a/src/bundler/options.rs b/src/bundler/options.rs
index af6271a8133f..e848bed2302c 100644
--- a/src/bundler/options.rs
+++ b/src/bundler/options.rs
@@ -2480,6 +2480,41 @@ pub enum PlaceholderField {
     Target,
 }
 
+/// `[dir]` placeholder value: relativize `source_dir` against `root_dir`.
+/// Canonicalizes `source_dir` via `get_fd_path` only when the plain string
+/// relativization falls outside `root_dir` and `on_disk` is set.
+pub(crate) fn source_dir_relative_to_root(
+    source_dir: &[u8],
+    root_dir: &[u8],
+    on_disk: bool,
+) -> Result<Box<[u8]>, bun_alloc::AllocError> {
+    use bun_paths::resolve_path;
+    // Empty for a bare-filename entry (`bun build hi.ts --external '*'`
+    // with no leading `./`); openat needs "." not "".
+    let source_dir: &[u8] = if source_dir.is_empty() {
+        b"."
+    } else {
+        source_dir
+    };
+    let rel = resolve_path::relative_platform::<resolve_path::platform::Auto, false>(
+        root_dir, source_dir,
+    );
+    if on_disk && rel.starts_with(b"..") {
+        let mut buf = bun_paths::path_buffer_pool::get();
+        if let Ok(f) = bun_sys::File::openat(
+            bun_sys::Fd::cwd(),
+            source_dir,
+            bun_sys::O::PATH | bun_sys::O::DIRECTORY,
+            0,
+        ) {
+            if let Ok(p) = f.get_path(&mut buf) {
+                return resolve_path::relative_alloc(root_dir, p);
+            }
+        }
+    }
+    Ok(Box::<[u8]>::from(rel))
+}
+
 // Shared body for PathTemplate::needs / PathTemplateConst::needs (D064).
 #[inline]
 pub(crate) fn path_template_needs(data: &[u8], field: PlaceholderField) -> bool {
diff --git a/test/bundler/bundler_naming.test.ts b/test/bundler/bundler_naming.test.ts
index a51451b19cbe..1f5a531d4f06 100644
--- a/test/bundler/bundler_naming.test.ts
+++ b/test/bundler/bundler_naming.test.ts
@@ -1,4 +1,7 @@
-import { describe } from "bun:test";
+import { describe, expect, test } from "bun:test";
+import { bunEnv, bunExe, isWindows, tempDir } from "harness";
+import { symlinkSync } from "node:fs";
+import { join } from "node:path";
 import { ESBUILD, itBundled } from "./expectBundled";
 
 describe("bundler", () => {
@@ -191,6 +194,108 @@ describe("bundler", () => {
       },
     ],
   });
+  // `[dir]` must resolve relative to the configured root even when root and
+  // the asset source path spell the same directory differently (Windows 8.3
+  // short names in the cwd, or a symlinked `Bun.build({ files })` key).
+  test("naming/AssetNamingDirCanonicalRoot", async () => {
+    using base = tempDir("asset-naming-dir-canon", {
+      "real/src/lib/first/.keep": "",
+      "real/src/lib/second/.keep": "",
+    });
+    const real = join(String(base), "real");
+    const link = join(String(base), "project-link");
+    // A junction needs no elevation on Windows; on POSIX this is a plain
+    // directory symlink. Either way `root` below canonicalizes to `real/src`
+    // while the `files` map keys keep the `project-link` spelling.
+    symlinkSync(real, link, isWindows ? "junction" : "dir");
+
+    const entry = join(link, "src/lib/first/file.js").replaceAll("\\", "/");
+    const asset = join(link, "src/lib/second/data.file").replaceAll("\\", "/");
+    const root = join(link, "src");
+
+    const script = `
+      const result = await Bun.build({
+        entrypoints: [${JSON.stringify(entry)}],
+        files: {
+          ${JSON.stringify(entry)}: 'import f from "../second/data.file"; console.log(f);',
+          ${JSON.stringify(asset)}: "this is a file",
+        },
+        root: ${JSON.stringify(root)},
+        naming: { entry: "hello.[ext]", asset: "[dir]/test.[ext]" },
+        loader: { ".file": "file" },
+      });
+      if (!result.success) {
+        for (const m of result.logs) console.error(String(m));
+        process.exit(1);
+      }
+      for (const out of result.outputs) console.log(out.kind + " " + out.path);
+    `;
+
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "-e", script],
+      env: bunEnv,
+      cwd: String(base),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+    const out = stdout.replaceAll("\\", "/");
+    const assetLine = out.split("\n").find(l => l.startsWith("asset "));
+    expect({ assetLine, stderr, exitCode }).toEqual({
+      assetLine: "asset ./lib/second/test.file",
+      stderr: "",
+      exitCode: 0,
+    });
+    expect(out).not.toContain("_.._");
+  });
+  // The on-disk canonicalization above must not apply to a plugin asset whose
+  // virtual path happens to collide with a real cwd subdirectory: `[dir]` for
+  // a non-file namespace stays a pure string computation.
+  test("naming/AssetNamingDirVirtualNamespace", async () => {
+    using base = tempDir("asset-naming-dir-virt", {
+      "src/.keep": "",
+      "unrelated-target/.keep": "",
+    });
+    symlinkSync(join(String(base), "unrelated-target"), join(String(base), "assets"), isWindows ? "junction" : "dir");
+
+    const entry = join(String(base), "src/entry.js").replaceAll("\\", "/");
+    const script = `
+      const result = await Bun.build({
+        entrypoints: [${JSON.stringify(entry)}],
+        files: { ${JSON.stringify(entry)}: 'import f from "virt:assets/icon.bin"; console.log(f);' },
+        root: ${JSON.stringify(join(String(base), "src"))},
+        naming: { entry: "hello.[ext]", asset: "[dir]/[name].[ext]" },
+        plugins: [{
+          name: "virt",
+          setup(b) {
+            b.onResolve({ filter: /^virt:/ }, a => ({ path: a.path.slice(5), namespace: "virt" }));
+            b.onLoad({ filter: /.*/, namespace: "virt" }, () => ({ contents: "hi", loader: "file" }));
+          },
+        }],
+      });
+      if (!result.success) { for (const m of result.logs) console.error(String(m)); process.exit(1); }
+      for (const out of result.outputs) console.log(out.kind + " " + out.path);
+    `;
+
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "-e", script],
+      env: bunEnv,
+      cwd: String(base),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+    const out = stdout.replaceAll("\\", "/");
+    const assetLine = out.split("\n").find(l => l.startsWith("asset "));
+    expect({ assetLine, stderr, exitCode }).toEqual({
+      assetLine: "asset ./_.._/assets/icon.bin",
+      stderr: "",
+      exitCode: 0,
+    });
+    expect(out).not.toContain("unrelated-target");
+  });
   itBundled("naming/AssetNoOverwrite", {
     todo: true,
     files: {