diff --git a/glimmer-scoped-css/src/ast-transform.ts b/glimmer-scoped-css/src/ast-transform.ts
index 0489a0d..b724d6d 100644
--- a/glimmer-scoped-css/src/ast-transform.ts
+++ b/glimmer-scoped-css/src/ast-transform.ts
@@ -9,6 +9,7 @@ import postcss from 'postcss';
 import scopedStylesPlugin from './postcss-plugin';
 import { basename } from 'path';
 import { GlimmerScopedCSSOptions } from '.';
+import { encodeCSS } from './encoding';
 
 type Env = WithJSUtils<ASTPluginEnvironment> & {
   filename: string;
@@ -76,7 +77,7 @@ export function generateScopedCSSPlugin(
             // TODO: hard coding the loader chain means we ignore the other
             // prevailing rules (and we're even assuming these loaders are
             // available)
-            let encodedCss = encodeURIComponent(btoa(outputCSS));
+            let encodedCss = encodeCSS(outputCSS);
 
             jsutils.importForSideEffect(
               `./${basename(env.filename)}.${encodedCss}.glimmer-scoped.css`
diff --git a/glimmer-scoped-css/src/encoding.ts b/glimmer-scoped-css/src/encoding.ts
new file mode 100644
index 0000000..77c3335
--- /dev/null
+++ b/glimmer-scoped-css/src/encoding.ts
@@ -0,0 +1,21 @@
+/**
+ * These functions convert between arbitrary normally formatted CSS and
+ * URI-safe strings that are used as data-URI virtual imports.
+ */
+
+// Adapted from https://developer.mozilla.org/en-US/docs/Web/API/Window/btoa#unicode_strings
+
+export function encodeCSS(plainCSSString: string) {
+  const binString = Array.from(
+    new TextEncoder().encode(plainCSSString),
+    (byte) => String.fromCodePoint(byte)
+  ).join('');
+  return encodeURIComponent(btoa(binString));
+}
+
+export function decodeCSS(encodedCSSString: string) {
+  const binString = atob(decodeURIComponent(encodedCSSString));
+  return new TextDecoder().decode(
+    Uint8Array.from(binString, (m) => m.codePointAt(0) as number)
+  );
+}
diff --git a/glimmer-scoped-css/src/index.ts b/glimmer-scoped-css/src/index.ts
index 3146f8f..0ba0f89 100644
--- a/glimmer-scoped-css/src/index.ts
+++ b/glimmer-scoped-css/src/index.ts
@@ -1,4 +1,5 @@
 import { generateScopedCSSPlugin } from './ast-transform';
+import { decodeCSS } from './encoding';
 
 export interface GlimmerScopedCSSOptions {
   noGlobal?: boolean;
@@ -40,5 +41,5 @@ export function decodeScopedCSSRequest(request: string): {
   if (!m) {
     throw new Error(`not a scoped CSS request: ${request}`);
   }
-  return { fromFile: m[1]!, css: atob(decodeURIComponent(m[2]!)) };
+  return { fromFile: m[1]!, css: decodeCSS(m[2]!) };
 }
diff --git a/test-app/app/components/multiple.gjs b/test-app/app/components/multiple.gjs
index 4044f07..ee8b35e 100644
--- a/test-app/app/components/multiple.gjs
+++ b/test-app/app/components/multiple.gjs
@@ -8,6 +8,10 @@ const MultipleInner = <template>
     p {
       font-weight: 700;
     }
+
+    p:before {
+      content: '✓';
+    }
   </style>
 </template>;
 
diff --git a/test-app/tests/acceptance/scoped-css-test.ts b/test-app/tests/acceptance/scoped-css-test.ts
index 55fc540..3cf041f 100644
--- a/test-app/tests/acceptance/scoped-css-test.ts
+++ b/test-app/tests/acceptance/scoped-css-test.ts
@@ -86,6 +86,17 @@ module('Acceptance | scoped css', function (hooks) {
       'font-weight': '700',
     });
 
+    const multipleInnerElement = find('[data-test-multiple-inner]');
+    const multipleInnerElementBeforeStyle = getComputedStyle(
+      multipleInnerElement!,
+      ':before'
+    );
+
+    assert.strictEqual(
+      multipleInnerElementBeforeStyle.getPropertyValue('content'),
+      '"✓"'
+    );
+
     assert.dom('[data-test-multiple-outer]').hasStyle({
       'font-style': 'italic',
       'font-weight': '900',