diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1898bb4a1a72..0a8ae44b83e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - _Upgrade (experimental)_: Ensure legacy theme values ending in `1` (like `theme(spacing.1)`) are correctly migrated to custom properties ([#14724](https://github.com/tailwindlabs/tailwindcss/pull/14724))
 - _Upgrade (experimental)_: Migrate arbitrary values to bare values for the `from-*`, `via-*`, and `to-*` utilities ([#14725](https://github.com/tailwindlabs/tailwindcss/pull/14725))
 - _Upgrade (experimental)_: Ensure `layer(utilities)` is removed from `@import` to keep `@utility` top-level ([#14738](https://github.com/tailwindlabs/tailwindcss/pull/14738))
+- _Upgrade (experimental)_: Ensure JS theme keys with special characters are escaped when migrated to CSS variables ([#14736](https://github.com/tailwindlabs/tailwindcss/pull/14736))
 - _Upgrade (experimental)_: Don't migrate important modifiers that are actually logical negations (e.g. `let foo = !border` to `let foo = border!`) ([#14737](https://github.com/tailwindlabs/tailwindcss/pull/14737))
 
 ### Changed
diff --git a/integrations/upgrade/js-config.test.ts b/integrations/upgrade/js-config.test.ts
index 17ebde28e0ea..9d2a6c5ee194 100644
--- a/integrations/upgrade/js-config.test.ts
+++ b/integrations/upgrade/js-config.test.ts
@@ -34,6 +34,57 @@ test(
               sm: ['0.875rem', { lineHeight: '1.5rem' }],
               base: ['1rem', { lineHeight: '2rem' }],
             },
+            width: {
+              px: '1px',
+              auto: 'auto',
+              1: '0.25rem',
+              1.5: '0.375rem',
+              2: '0.5rem',
+              2.5: '0.625rem',
+              3: '0.75rem',
+              3.5: '0.875rem',
+              4: '1rem',
+              5: '1.25rem',
+              6: '1.5rem',
+              8: '2rem',
+              10: '2.5rem',
+              11: '2.75rem',
+              12: '3rem',
+              16: '4rem',
+              24: '6rem',
+              32: '8rem',
+              40: '10rem',
+              48: '12rem',
+              64: '16rem',
+              80: '20rem',
+              96: '24rem',
+              128: '32rem',
+
+              full: '100%',
+              0: '0%',
+              '1/2': '50%',
+              '1/3': 'calc(100% / 3)',
+              '2/3': 'calc(100% / 3 * 2)',
+              '1/4': '25%',
+              '3/4': '75%',
+              '1/5': '20%',
+              '2/5': '40%',
+              '3/5': '60%',
+              '4/5': '80%',
+              '1/6': 'calc(100% / 6)',
+              '5/6': 'calc(100% / 6 * 5)',
+              '1/7': 'calc(100% / 7)',
+              '1/10': 'calc(100% / 10)',
+              '3/10': 'calc(100% / 10 * 3)',
+              '7/10': 'calc(100% / 10 * 7)',
+              '9/10': 'calc(100% / 10 * 9)',
+              screen: '100vw',
+
+              'full-minus-80': 'calc(100% - 20rem)',
+              'full-minus-96': 'calc(100% - 24rem)',
+
+              '225px': '225px',
+            },
             extend: {
               colors: {
                 red: {
@@ -147,6 +198,54 @@ test(
         --font-size-base: 1rem;
         --font-size-base--line-height: 2rem;
 
+        --width-*: initial;
+        --width-0: 0%;
+        --width-1: 0.25rem;
+        --width-2: 0.5rem;
+        --width-3: 0.75rem;
+        --width-4: 1rem;
+        --width-5: 1.25rem;
+        --width-6: 1.5rem;
+        --width-8: 2rem;
+        --width-10: 2.5rem;
+        --width-11: 2.75rem;
+        --width-12: 3rem;
+        --width-16: 4rem;
+        --width-24: 6rem;
+        --width-32: 8rem;
+        --width-40: 10rem;
+        --width-48: 12rem;
+        --width-64: 16rem;
+        --width-80: 20rem;
+        --width-96: 24rem;
+        --width-128: 32rem;
+        --width-px: 1px;
+        --width-auto: auto;
+        --width-1_5: 0.375rem;
+        --width-2_5: 0.625rem;
+        --width-3_5: 0.875rem;
+        --width-full: 100%;
+        --width-1\\/2: 50%;
+        --width-1\\/3: calc(100% / 3);
+        --width-2\\/3: calc(100% / 3 * 2);
+        --width-1\\/4: 25%;
+        --width-3\\/4: 75%;
+        --width-1\\/5: 20%;
+        --width-2\\/5: 40%;
+        --width-3\\/5: 60%;
+        --width-4\\/5: 80%;
+        --width-1\\/6: calc(100% / 6);
+        --width-5\\/6: calc(100% / 6 * 5);
+        --width-1\\/7: calc(100% / 7);
+        --width-1\\/10: calc(100% / 10);
+        --width-3\\/10: calc(100% / 10 * 3);
+        --width-7\\/10: calc(100% / 10 * 7);
+        --width-9\\/10: calc(100% / 10 * 9);
+        --width-screen: 100vw;
+        --width-full-minus-80: calc(100% - 20rem);
+        --width-full-minus-96: calc(100% - 24rem);
+        --width-225px: 225px;
+
         --font-family-sans: Inter, system-ui, sans-serif;
         --font-family-display: Cabinet Grotesk, ui-sans-serif, system-ui, sans-serif,
           'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';
diff --git a/packages/@tailwindcss-upgrade/src/migrate-js-config.ts b/packages/@tailwindcss-upgrade/src/migrate-js-config.ts
index 20f7fdd7f53c..f8a6ad6f8dc2 100644
--- a/packages/@tailwindcss-upgrade/src/migrate-js-config.ts
+++ b/packages/@tailwindcss-upgrade/src/migrate-js-config.ts
@@ -15,6 +15,7 @@ import { resolveConfig, type ConfigFile } from '../../tailwindcss/src/compat/con
 import type { ThemeConfig } from '../../tailwindcss/src/compat/config/types'
 import { darkModePlugin } from '../../tailwindcss/src/compat/dark-mode'
 import type { DesignSystem } from '../../tailwindcss/src/design-system'
+import { escape } from '../../tailwindcss/src/utils/escape'
 import { findStaticPlugins, type StaticPluginOptions } from './utils/extract-static-plugins'
 import { info } from './utils/renderer'
 
@@ -121,10 +122,16 @@ async function migrateTheme(
 
     if (resetNamespaces.has(key[0]) && resetNamespaces.get(key[0]) === false) {
       resetNamespaces.set(key[0], true)
-      css += `  --${keyPathToCssProperty([key[0]])}-*: initial;\n`
+      let property = keyPathToCssProperty([key[0]])
+      if (property !== null) {
+        css += `  ${escape(`--${property}`)}-*: initial;\n`
+      }
     }
 
-    css += `  --${keyPathToCssProperty(key)}: ${value};\n`
+    let property = keyPathToCssProperty(key)
+    if (property !== null) {
+      css += `  ${escape(`--${property}`)}: ${value};\n`
+    }
   }
 
   if ('keyframes' in resolvedConfig.theme) {
diff --git a/packages/tailwindcss/src/compat/apply-config-to-theme.test.ts b/packages/tailwindcss/src/compat/apply-config-to-theme.test.ts
index 4adbce09d75b..9cb5782f4423 100644
--- a/packages/tailwindcss/src/compat/apply-config-to-theme.test.ts
+++ b/packages/tailwindcss/src/compat/apply-config-to-theme.test.ts
@@ -1,7 +1,7 @@
-import { expect, test } from 'vitest'
+import { describe, expect, test } from 'vitest'
 import { buildDesignSystem } from '../design-system'
 import { Theme, ThemeOptions } from '../theme'
-import { applyConfigToTheme } from './apply-config-to-theme'
+import { applyConfigToTheme, keyPathToCssProperty } from './apply-config-to-theme'
 import { resolveConfig } from './config/resolve-config'
 
 test('config values can be merged into the theme', () => {
@@ -157,3 +157,12 @@ test('invalid keys are not merged into the theme', () => {
 
   expect(entries.length).toEqual(0)
 })
+
+describe('keyPathToCssProperty', () => {
+  test.each([
+    [['width', '40', '2/5'], '--width-40-2/5'],
+    [['spacing', '0.5'], '--spacing-0_5'],
+  ])('converts %s to %s', (keyPath, expected) => {
+    expect(`--${keyPathToCssProperty(keyPath)}`).toEqual(expected)
+  })
+})