diff --git a/CHANGELOG.md b/CHANGELOG.md
index a345e26cd821..8348aba4d4a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -39,6 +39,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - _Upgrade (experimental)_: Install `@tailwindcss/postcss` next to `tailwindcss` ([#14830](https://github.com/tailwindlabs/tailwindcss/pull/14830))
 - _Upgrade (experimental)_: Remove whitespace around `,` separator when print arbitrary values ([#14838](https://github.com/tailwindlabs/tailwindcss/pull/14838))
 - _Upgrade (experimental)_: Fix crash during upgrade when content globs escape root of project ([#14896](https://github.com/tailwindlabs/tailwindcss/pull/14896))
+- _Upgrade (experimental)_: Don't convert `theme(…/15%)` to modifier unless it is the entire arbitrary value of a utility ([#14922](https://github.com/tailwindlabs/tailwindcss/pull/14922))
 
 ### Changed
 
diff --git a/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.test.ts b/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.test.ts
index 0e6850672586..2bad8ba80912 100644
--- a/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.test.ts
+++ b/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.test.ts
@@ -77,6 +77,13 @@ test.each([
   // Arbitrary property that already contains a modifier
   ['[color:theme(colors.red.500/50%)]/50', '[color:theme(--color-red-500/50%)]/50'],
 
+  // Values that don't contain only `theme(…)` calls should not be converted to
+  // use a modifier since the color is not the whole value.
+  [
+    'shadow-[shadow:inset_0px_1px_theme(colors.white/15%)]',
+    'shadow-[shadow:inset_0px_1px_theme(--color-white/15%)]',
+  ],
+
   // Arbitrary value, where the candidate already contains a modifier
   // This should still migrate the `theme(…)` syntax to the modern syntax.
   ['bg-[theme(colors.red.500/50%)]/50', 'bg-[theme(--color-red-500/50%)]/50'],
diff --git a/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.ts b/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.ts
index 78b4ee2c62f9..c1eb986288e0 100644
--- a/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.ts
+++ b/packages/@tailwindcss-upgrade/src/template/codemods/theme-to-var.ts
@@ -158,7 +158,12 @@ export function createConverter(designSystem: DesignSystem, { prettyPrint = fals
       // Currently, we are assuming that this is only being used for colors,
       // which means that we can typically convert them to a modifier on the
       // candidate itself.
-      if (parts.length === 2 && options & Convert.MigrateModifier) {
+      //
+      // If there is more than one node in the AST though, `theme(…)` must not
+      // be the whole value so it's not safe to use a modifier instead.
+      //
+      // E.g.: `inset 0px 1px theme(colors.red.500/50%)` is a shadow, not a color.
+      if (ast.length === 1 && parts.length === 2 && options & Convert.MigrateModifier) {
         let [pathPart, modifierPart] = parts
 
         // 50% -> /50