diff --git a/index.js b/index.js
index 3a062db..3bd4293 100644
--- a/index.js
+++ b/index.js
@@ -160,10 +160,11 @@ export class DomStack {
     this.#src = src
     this.#dest = dest
 
-    const copyDirs = opts?.copy ?? []
+    const copyDirs = (opts?.copy ?? []).map(dir => resolve(dir))
 
     this.opts = {
       ...opts,
+      copy: copyDirs,
       ignore: [
         ...DEFAULT_IGNORES,
         basename(dest),
@@ -172,12 +173,11 @@ export class DomStack {
       ],
     }
 
-    if (copyDirs && copyDirs.length > 0) {
+    if (copyDirs.length > 0) {
       const absDest = resolve(this.#dest)
       for (const copyDir of copyDirs) {
         // Copy dirs can be in the src dir (nested builds), but not in the dest dir.
-        const absCopyDir = resolve(copyDir)
-        const relToDest = relative(absDest, absCopyDir)
+        const relToDest = relative(absDest, copyDir)
         if (relToDest === '' || !relToDest.startsWith('..')) {
           throw new Error(`copyDir ${copyDir} is within the dest directory`)
         }
diff --git a/test-cases/constructor-copy-paths/index.test.js b/test-cases/constructor-copy-paths/index.test.js
new file mode 100644
index 0000000..b43af32
--- /dev/null
+++ b/test-cases/constructor-copy-paths/index.test.js
@@ -0,0 +1,41 @@
+import { test } from 'node:test'
+import assert from 'node:assert'
+import { isAbsolute, resolve, join } from 'node:path'
+import { tmpdir } from 'node:os'
+import { DomStack } from '../../index.js'
+
+const tmpSrc = join(tmpdir(), 'domstack-test-src')
+const tmpDest = join(tmpdir(), 'domstack-test-dest')
+
+test.describe('DomStack constructor - copy path resolution', () => {
+  test('resolves a relative copy path to an absolute path', () => {
+    const ds = new DomStack(tmpSrc, tmpDest, {
+      copy: ['some-relative-copy-dir'],
+    })
+
+    assert.strictEqual(ds.opts.copy.length, 1, 'one copy entry')
+    const copyPath = /** @type {string} */ (ds.opts.copy[0])
+    assert.ok(isAbsolute(copyPath), `copy path should be absolute, got: "${copyPath}"`)
+  })
+
+  test('leaves an already-absolute copy path normalized', () => {
+    const absPath = join(tmpdir(), 'absolute', 'copy', 'dir')
+    const ds = new DomStack(tmpSrc, tmpDest, {
+      copy: [absPath],
+    })
+
+    assert.strictEqual(ds.opts.copy[0], resolve(absPath), 'absolute path is preserved and normalized')
+  })
+
+  test('resolves multiple mixed copy paths', () => {
+    const absPath = join(tmpdir(), 'absolute', 'dir')
+    const ds = new DomStack(tmpSrc, tmpDest, {
+      copy: ['relative-dir', absPath],
+    })
+
+    assert.strictEqual(ds.opts.copy.length, 2, 'two copy entries')
+    for (const p of ds.opts.copy) {
+      assert.ok(isAbsolute(p), `each copy path should be absolute, got: "${p}"`)
+    }
+  })
+})