diff --git a/CHANGELOG.md b/CHANGELOG.md
index c2686352696a..7ff6cdbb6bc3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,11 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
-
 ### Fixed
 
 - Ensure that the `containers` JS theme key is added to the `--container-*` namespace. ([#16169](https://github.com/tailwindlabs/tailwindcss/pull/16169))
+- Fix missing `@keyframes` definition ([#16237](https://github.com/tailwindlabs/tailwindcss/pull/16237))
 
 ## [4.0.3] - 2025-02-01
 
diff --git a/packages/tailwindcss/src/index.test.ts b/packages/tailwindcss/src/index.test.ts
index 67a0a3d64dab..497ccc034173 100644
--- a/packages/tailwindcss/src/index.test.ts
+++ b/packages/tailwindcss/src/index.test.ts
@@ -1170,6 +1170,45 @@ describe('Parsing themes values from CSS', () => {
     `)
   })
 
+  test('`@keyframes` in `@theme` are generated when name contains a new line', async () => {
+    expect(
+      await compileCss(
+        css`
+          @theme {
+            --animate-very-long-animation-name: very-long-animation-name
+              var(
+                --very-long-animation-name-configuration,
+                2.5s ease-in-out 0s infinite normal none running
+              );
+
+            @keyframes very-long-animation-name {
+              to {
+                opacity: 1;
+              }
+            }
+          }
+
+          @tailwind utilities;
+        `,
+        ['animate-very-long-animation-name'],
+      ),
+    ).toMatchInlineSnapshot(`
+      ":root, :host {
+        --animate-very-long-animation-name: very-long-animation-name var(--very-long-animation-name-configuration, 2.5s ease-in-out 0s infinite normal none running);
+      }
+
+      .animate-very-long-animation-name {
+        animation: var(--animate-very-long-animation-name);
+      }
+
+      @keyframes very-long-animation-name {
+        to {
+          opacity: 1;
+        }
+      }"
+    `)
+  })
+
   test('`@theme` values can be unset', async () => {
     expect(
       await compileCss(
diff --git a/packages/tailwindcss/src/index.ts b/packages/tailwindcss/src/index.ts
index 2baed9acf6a5..37c19a3f3edf 100644
--- a/packages/tailwindcss/src/index.ts
+++ b/packages/tailwindcss/src/index.ts
@@ -545,7 +545,7 @@ async function parseCss(
     let keyframesRules = theme.getKeyframes()
     if (keyframesRules.length > 0) {
       let animationParts = [...theme.namespace('--animate').values()].flatMap((animation) =>
-        animation.split(' '),
+        animation.split(/\s+/),
       )
 
       for (let keyframesRule of keyframesRules) {