diff --git a/README.md b/README.md
index 0062e43..dac52f0 100644
--- a/README.md
+++ b/README.md
@@ -334,6 +334,10 @@ const styles = await css('./src/routes/page.tsx', {
 
 This keeps `@knighted/css` resolution in sync with your bundler’s alias/extension rules.
 
+### Sass alias specifiers
+
+If your Sass files rely on virtual specifiers such as `pkg:#styles/modules/typography.scss`, forward the same resolver you use for JavaScript imports. `@knighted/css` normalizes any resolver-backed custom scheme to a real `file://` URL before Dart Sass evaluates it, so a file loaded via `pkg:#…` still has a stable canonical URL. That keeps Sass’s internal `new URL('./tokens.scss', context.containingUrl)` calls working, which means relative `@use`/`@import` statements inside those alias-backed files continue to resolve just like they do in your bundler.
+
 ### Specificity boost
 
 Use `specificityBoost` to tweak selector behavior:
diff --git a/package-lock.json b/package-lock.json
index 9df1652..064938f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11041,7 +11041,7 @@
     },
     "packages/css": {
       "name": "@knighted/css",
-      "version": "1.0.0-rc.4",
+      "version": "1.0.0-rc.5",
       "license": "MIT",
       "dependencies": {
         "dependency-tree": "^11.2.0",
@@ -11068,7 +11068,7 @@
       "name": "@knighted/css-playwright-fixture",
       "version": "0.0.0",
       "dependencies": {
-        "@knighted/css": "1.0.0-rc.4",
+        "@knighted/css": "1.0.0-rc.5",
         "@knighted/jsx": "^1.2.1",
         "lit": "^3.2.1",
         "react": "^19.0.0",
diff --git a/packages/css/package.json b/packages/css/package.json
index b33def0..8c3bc9f 100644
--- a/packages/css/package.json
+++ b/packages/css/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@knighted/css",
-  "version": "1.0.0-rc.4",
+  "version": "1.0.0-rc.5",
   "description": "A build-time utility that traverses JavaScript/TypeScript module dependency graphs to extract, compile, and optimize all imported CSS into a single, in-memory string.",
   "type": "module",
   "main": "./dist/css.js",
diff --git a/packages/css/src/css.ts b/packages/css/src/css.ts
index 9c8122d..766f8e9 100644
--- a/packages/css/src/css.ts
+++ b/packages/css/src/css.ts
@@ -1,5 +1,6 @@
 import path from 'node:path'
 import { existsSync, promises as fs } from 'node:fs'
+import { fileURLToPath, pathToFileURL } from 'node:url'
 
 import dependencyTree from 'dependency-tree'
 import type { Options as DependencyTreeOpts } from 'dependency-tree'
@@ -92,6 +93,7 @@ export async function cssWithMeta(
     const chunk = await compileStyleModule(file, {
       cwd,
       peerResolver: options.peerResolver,
+      resolver: options.resolver,
     })
     if (chunk) {
       chunks.push(chunk)
@@ -198,14 +200,22 @@ function matchExtension(filePath: string, extensions: string[]): string | undefi
 
 async function compileStyleModule(
   file: StyleModule,
-  { cwd, peerResolver }: { cwd: string; peerResolver?: PeerLoader },
+  {
+    cwd,
+    peerResolver,
+    resolver,
+  }: { cwd: string; peerResolver?: PeerLoader; resolver?: CssResolver },
 ): Promise<string> {
   switch (file.ext) {
     case '.css':
       return fs.readFile(file.path, 'utf8')
     case '.scss':
     case '.sass':
-      return compileSass(file.path, file.ext === '.sass', peerResolver)
+      return compileSass(file.path, file.ext === '.sass', {
+        cwd,
+        peerResolver,
+        resolver,
+      })
     case '.less':
       return compileLess(file.path, peerResolver)
     case '.css.ts':
@@ -218,7 +228,11 @@ async function compileStyleModule(
 async function compileSass(
   filePath: string,
   indented: boolean,
-  peerResolver?: PeerLoader,
+  {
+    cwd,
+    peerResolver,
+    resolver,
+  }: { cwd: string; peerResolver?: PeerLoader; resolver?: CssResolver },
 ): Promise<string> {
   const sassModule = await optionalPeer<typeof import('sass')>(
     'sass',
@@ -226,9 +240,11 @@ async function compileSass(
     peerResolver,
   )
   const sass = sassModule
-  const result = sass.compile(filePath, {
+  const importer = createSassImporter({ cwd, resolver })
+  const result = await sass.compileAsync(filePath, {
     style: 'expanded',
     loadPaths: buildSassLoadPaths(filePath),
+    importers: importer ? [importer] : undefined,
   })
   return result.css
 }
@@ -253,6 +269,132 @@ function buildSassLoadPaths(filePath: string): string[] {
   return Array.from(loadPaths).filter(dir => dir && existsSync(dir))
 }
 
+function createSassImporter({ cwd, resolver }: { cwd: string; resolver?: CssResolver }) {
+  if (!resolver) return undefined
+  const debug = process.env.KNIGHTED_CSS_DEBUG_SASS === '1'
+
+  return {
+    async canonicalize(url: string, context?: { containingUrl?: URL | null }) {
+      if (debug) {
+        console.error('[knighted-css:sass] canonicalize request:', url)
+        if (context?.containingUrl) {
+          console.error('[knighted-css:sass] containing url:', context.containingUrl.href)
+        }
+      }
+      if (shouldNormalizeSpecifier(url)) {
+        const resolvedPath = await resolveAliasSpecifier(url, resolver, cwd)
+        if (!resolvedPath) {
+          if (debug) {
+            console.error('[knighted-css:sass] resolver returned no result for', url)
+          }
+          return null
+        }
+        const fileUrl = pathToFileURL(resolvedPath)
+        if (debug) {
+          console.error('[knighted-css:sass] canonical url:', fileUrl.href)
+        }
+        return fileUrl
+      }
+      const relativePath = resolveRelativeSpecifier(url, context?.containingUrl)
+      if (relativePath) {
+        const fileUrl = pathToFileURL(relativePath)
+        if (debug) {
+          console.error('[knighted-css:sass] canonical url:', fileUrl.href)
+        }
+        return fileUrl
+      }
+      return null
+    },
+    async load(canonicalUrl: URL) {
+      if (debug) {
+        console.error('[knighted-css:sass] load request:', canonicalUrl.href)
+      }
+      const filePath = fileURLToPath(canonicalUrl)
+      const contents = await fs.readFile(filePath, 'utf8')
+      return {
+        contents,
+        syntax: inferSassSyntax(filePath),
+      }
+    },
+  }
+}
+
+async function resolveAliasSpecifier(
+  specifier: string,
+  resolver: CssResolver,
+  cwd: string,
+): Promise<string | undefined> {
+  const resolved = await resolver(specifier, { cwd })
+  if (!resolved) {
+    return undefined
+  }
+  if (resolved.startsWith('file://')) {
+    return ensureSassPath(fileURLToPath(new URL(resolved)))
+  }
+  const normalized = path.isAbsolute(resolved) ? resolved : path.resolve(cwd, resolved)
+  return ensureSassPath(normalized)
+}
+
+function shouldNormalizeSpecifier(specifier: string): boolean {
+  const schemeMatch = specifier.match(/^([a-z][\w+.-]*):/i)
+  if (!schemeMatch) {
+    return false
+  }
+  const scheme = schemeMatch[1].toLowerCase()
+  if (
+    scheme === 'file' ||
+    scheme === 'http' ||
+    scheme === 'https' ||
+    scheme === 'data' ||
+    scheme === 'sass'
+  ) {
+    return false
+  }
+  return true
+}
+
+function inferSassSyntax(filePath: string): 'scss' | 'indented' {
+  return filePath.endsWith('.sass') ? 'indented' : 'scss'
+}
+
+function ensureSassPath(filePath: string): string | undefined {
+  if (existsSync(filePath)) {
+    return filePath
+  }
+  const ext = path.extname(filePath)
+  const dir = path.dirname(filePath)
+  const base = path.basename(filePath, ext)
+  const partialCandidate = path.join(dir, `_${base}${ext}`)
+  if (ext && existsSync(partialCandidate)) {
+    return partialCandidate
+  }
+  const indexCandidate = path.join(dir, base, `index${ext}`)
+  if (ext && existsSync(indexCandidate)) {
+    return indexCandidate
+  }
+  const partialIndexCandidate = path.join(dir, base, `_index${ext}`)
+  if (ext && existsSync(partialIndexCandidate)) {
+    return partialIndexCandidate
+  }
+  return undefined
+}
+
+function resolveRelativeSpecifier(
+  specifier: string,
+  containingUrl?: URL | null,
+): string | undefined {
+  if (!containingUrl || containingUrl.protocol !== 'file:') {
+    return undefined
+  }
+  if (/^[a-z][\w+.-]*:/i.test(specifier)) {
+    return undefined
+  }
+  const containingPath = fileURLToPath(containingUrl)
+  const baseDir = path.dirname(containingPath)
+  const candidate = path.resolve(baseDir, specifier)
+  return ensureSassPath(candidate)
+}
+
 async function compileLess(filePath: string, peerResolver?: PeerLoader): Promise<string> {
   const mod = await optionalPeer<typeof import('less')>('less', 'Less', peerResolver)
   const less = unwrapModuleNamespace(mod)
diff --git a/packages/css/test/css.test.ts b/packages/css/test/css.test.ts
index f9b6f77..0e61d1f 100644
--- a/packages/css/test/css.test.ts
+++ b/packages/css/test/css.test.ts
@@ -18,6 +18,8 @@ const vanillaEntry = path.join(fixturesDir, 'vanilla/styles.css.ts')
 const miscFixturesDir = path.resolve(__dirname, './fixtures/misc')
 const selectorsCss = path.join(miscFixturesDir, 'selectors.css')
 const unsupportedStyle = path.join(miscFixturesDir, 'unsupported.noop')
+const pkgAliasDir = path.resolve(__dirname, './fixtures/pkg-alias')
+const pkgAliasEntry = path.join(pkgAliasDir, 'entry.scss')
 
 test('extracts CSS from JS dependency graph', async () => {
   const result = await css(basicEntry)
@@ -41,6 +43,19 @@ test('supports indented sass compilation', async () => {
   assert.match(result, /padding-inline:\s*1\.25rem/)
 })
 
+test('normalizes custom scheme specifiers before Sass resolves relatives', async () => {
+  const result = await css(pkgAliasEntry, {
+    resolver: async specifier => {
+      if (!specifier.startsWith('pkg:#')) return undefined
+      const relativePath = specifier.replace(/^pkg:#/, '')
+      return path.join(pkgAliasDir, relativePath)
+    },
+  })
+
+  assert.match(result, /\.alias-demo/)
+  assert.match(result, /font-family:\s*["']Space Grotesk["'], sans-serif/)
+})
+
 test('supports less compilation', async () => {
   const result = await css(lessEntry)
   assert.match(result, /\.less-styles/)
diff --git a/packages/css/test/fixtures/pkg-alias/entry.scss b/packages/css/test/fixtures/pkg-alias/entry.scss
new file mode 100644
index 0000000..1ae8c39
--- /dev/null
+++ b/packages/css/test/fixtures/pkg-alias/entry.scss
@@ -0,0 +1,6 @@
+@use 'pkg:#styles/modules/typography.scss' as typography;
+
+.alias-demo {
+  @include typography.apply-stack;
+  font-size: 1rem;
+}
diff --git a/packages/css/test/fixtures/pkg-alias/styles/modules/_tokens.scss b/packages/css/test/fixtures/pkg-alias/styles/modules/_tokens.scss
new file mode 100644
index 0000000..885b926
--- /dev/null
+++ b/packages/css/test/fixtures/pkg-alias/styles/modules/_tokens.scss
@@ -0,0 +1 @@
+$base-stack: 'Space Grotesk', sans-serif;
diff --git a/packages/css/test/fixtures/pkg-alias/styles/modules/_typography.scss b/packages/css/test/fixtures/pkg-alias/styles/modules/_typography.scss
new file mode 100644
index 0000000..b3fcabd
--- /dev/null
+++ b/packages/css/test/fixtures/pkg-alias/styles/modules/_typography.scss
@@ -0,0 +1,7 @@
+@use './tokens.scss';
+
+$stack: tokens.$base-stack;
+
+@mixin apply-stack {
+  font-family: $stack;
+}
diff --git a/packages/playwright/package.json b/packages/playwright/package.json
index 20df54f..5392d88 100644
--- a/packages/playwright/package.json
+++ b/packages/playwright/package.json
@@ -14,7 +14,7 @@
     "pretest": "npm run build"
   },
   "dependencies": {
-    "@knighted/css": "1.0.0-rc.4",
+    "@knighted/css": "1.0.0-rc.5",
     "@knighted/jsx": "^1.2.1",
     "lit": "^3.2.1",
     "react": "^19.0.0",