diff --git a/src/plugins/transform.ts b/src/plugins/transform.ts
index 3cc4da5..00a4329 100644
--- a/src/plugins/transform.ts
+++ b/src/plugins/transform.ts
@@ -39,16 +39,29 @@ export const FontFamilyInjectionPlugin = (options: FontFamilyInjectionPluginOpti
         }
       }
 
-      // TODO: handle these edge cases
-      // 1. existing font-family in this scope
-      // 2. handle CSS custom properties
-      walk(parse(code), {
+      const ast = parse(code)
+
+      // Collect existing `@font-face` declarations (to skip adding them)
+      const existingFontFamilies = new Set<string>()
+      walk(ast, {
+        visit: 'Declaration',
+        enter (node) {
+          if (this.atrule?.name === 'font-face' && node.property === 'font-family') {
+            for (const family of extractFontFamilies(node)) {
+              existingFontFamilies.add(family)
+            }
+          }
+        }
+      })
+
+      // TODO: handle CSS custom properties
+      walk(ast, {
         visit: 'Declaration',
         enter (node) {
           if (node.property !== 'font-family' || this.atrule?.name === 'font-face') { return }
 
           for (const fontFamily of extractFontFamilies(node)) {
-            if (processedFontFamilies.has(fontFamily)) continue
+            if (processedFontFamilies.has(fontFamily) || existingFontFamilies.has(fontFamily)) continue
             processedFontFamilies.add(fontFamily)
             promises.push(addFontFaceDeclaration(fontFamily))
           }
diff --git a/test/parse.test.ts b/test/parse.test.ts
index 6cbf9d7..259a912 100644
--- a/test/parse.test.ts
+++ b/test/parse.test.ts
@@ -2,28 +2,47 @@ import { describe, expect, it } from 'vitest'
 import { FontFamilyInjectionPlugin } from '../src/plugins/transform'
 
 describe('parsing', () => {
-  it('should declarations within `@font-face`', async () => {
+  it('should add declarations for `font-family`', async () => {
+    expect(await transform(`:root { font-family: 'CustomFont' }`))
+      .toMatchInlineSnapshot(`
+        "@font-face {
+          font-family: 'CustomFont';
+          src: url("/customfont.woff2") format(woff2);
+          font-display: swap;
+        }
+        :root { font-family: 'CustomFont' }"
+      `)
+  })
+
+  it('should skip processing declarations within `@font-face`', async () => {
     expect(await transform(`@font-face { font-family: 'CustomFont' }`))
       .toMatchInlineSnapshot(`undefined`)
   })
 
-  it('should add declarations for `font-family`', async () => {
-    expect(await transform(`:root { font-family: 'CustomFont' }`))
+  it('should ignore any @font-face already in scope', async () => {
+    expect(await transform([
+      `@font-face { font-family: 'ScopedFont'; src: local("ScopedFont") }`,
+      `:root { font-family: 'ScopedFont' }`,
+      `:root { font-family: 'CustomFont' }`,
+    ].join('\n')))
       .toMatchInlineSnapshot(`
         "@font-face {
           font-family: 'CustomFont';
-          src: url("/font.woff2") format(woff2);
+          src: url("/customfont.woff2") format(woff2);
           font-display: swap;
         }
+        @font-face { font-family: 'ScopedFont'; src: local("ScopedFont") }
+        :root { font-family: 'ScopedFont' }
         :root { font-family: 'CustomFont' }"
       `)
   })
 })
 
-
+const slugify = (str: string) => str.toLowerCase().replace(/[^\d\w]/g, '-')
 async function transform (css: string) {
-  const plugin = FontFamilyInjectionPlugin({ resolveFontFace: () => ({ src: '/font.woff2' }) })
-    .raw({}, { framework: 'vite' }) as any
+  const plugin = FontFamilyInjectionPlugin({
+    resolveFontFace: (family) => ({ src: `/${slugify(family)}.woff2` })
+  }).raw({}, { framework: 'vite' }) as any
 
   const result = await plugin.transform(css)
   return result?.code