diff --git a/packages/compiler/src/shadow_css.ts b/packages/compiler/src/shadow_css.ts
index 92ec3807d96..be70d3d3104 100644
--- a/packages/compiler/src/shadow_css.ts
+++ b/packages/compiler/src/shadow_css.ts
@@ -362,7 +362,7 @@ export class ShadowCss {
     unscopedKeyframesSet: ReadonlySet<string>,
   ): CssRule {
     let content = rule.content.replace(
-      /((?:^|\s+|;)(?:-webkit-)?animation\s*:\s*)([^;]+)/g,
+      /((?:^|[\s;{])(?:-webkit-)?animation\s*:\s*)([^;}]+)/g,
       (_, start, animationDeclarations) =>
         start +
         animationDeclarations.replace(
@@ -393,7 +393,7 @@ export class ShadowCss {
         ),
     );
     content = content.replace(
-      /((?:^|\s+|;)(?:-webkit-)?animation-name(?:\s*):(?:\s*))([^;]+)/g,
+      /((?:^|[\s;{])(?:-webkit-)?animation-name(?:\s*):(?:\s*))([^;}]+)/g,
       (_match, start, commaSeparatedKeyframes) =>
         `${start}${commaSeparatedKeyframes
           .split(',')
diff --git a/packages/compiler/test/shadow_css/keyframes_spec.ts b/packages/compiler/test/shadow_css/keyframes_spec.ts
index b03e7da4907..884af6bbcc2 100644
--- a/packages/compiler/test/shadow_css/keyframes_spec.ts
+++ b/packages/compiler/test/shadow_css/keyframes_spec.ts
@@ -259,6 +259,17 @@ describe('ShadowCss, keyframes and animations', () => {
     expect(shim(css, 'host-a')).toEqual(expected);
   });
 
+  it('should correctly process animations defined in minified rules nested in an at-rule', () => {
+    let css = '@keyframes foo {}@media screen{.test{animation:foo 1s forwards}}';
+    let expected =
+      '@keyframes host-a_foo {}@media screen{.test[host-a]{animation:host-a_foo 1s forwards}}';
+    expect(shim(css, 'host-a')).toEqual(expected);
+    css = '@keyframes foo {}@supports (display:grid){.test{animation-name:foo}}';
+    expected =
+      '@keyframes host-a_foo {}@supports (display:grid){.test[host-a]{animation-name:host-a_foo}}';
+    expect(shim(css, 'host-a')).toEqual(expected);
+  });
+
   it('should ignore keywords values when scoping local animations', () => {
     const css = `
         div {