diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3c161e571aa8..4d7a1fcbeb31 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Handle `'` syntax in ClojureScript when extracting classes ([#18888](https://github.com/tailwindlabs/tailwindcss/pull/18888))
 - Handle `@variant` inside `@custom-variant` ([#18885](https://github.com/tailwindlabs/tailwindcss/pull/18885))
+- Merge suggestions when using `@utility` ([#18900](https://github.com/tailwindlabs/tailwindcss/pull/18900))
 
 ## [4.1.13] - 2025-09-03
 
diff --git a/packages/tailwindcss/src/intellisense.test.ts b/packages/tailwindcss/src/intellisense.test.ts
index 32893b1a0c8e..5dbfc8c54c80 100644
--- a/packages/tailwindcss/src/intellisense.test.ts
+++ b/packages/tailwindcss/src/intellisense.test.ts
@@ -572,6 +572,39 @@ test('Custom functional @utility', async () => {
   expect(classMap.get('example-xs')?.modifiers).toEqual(['normal', 'foo', 'bar'])
 })
 
+test('Custom utilities sharing a root with built-in utilities should merge suggestions', async () => {
+  let input = css`
+    @import 'tailwindcss/utilities';
+    @theme {
+      --font-sans: sans-serif;
+    }
+
+    @theme {
+      --font-weight-custom: 1234;
+      --font-weight-bold: bold; /* Overlap with existing utility */
+    }
+
+    @utility font-* {
+      --my-font-weight: --value(--font-weight- *);
+    }
+  `
+
+  let design = await __unstable__loadDesignSystem(input, {
+    loadStylesheet: async (_, base) => ({
+      path: '',
+      base,
+      content: '@tailwind utilities;',
+    }),
+  })
+
+  let classMap = new Map(design.getClassList())
+  let classNames = Array.from(classMap.keys())
+
+  expect(classNames).toContain('font-sans') // Existing font-family utility
+  expect(classNames).toContain('font-bold') // Existing font-family utility & custom font-weight utility
+  expect(classNames).toContain('font-custom') // Custom font-weight utility
+})
+
 test('Theme keys with underscores are suggested with underscores', async () => {
   let input = css`
     @import 'tailwindcss/utilities';
diff --git a/packages/tailwindcss/src/intellisense.ts b/packages/tailwindcss/src/intellisense.ts
index 27db3a540bc3..e6db73b50f4a 100644
--- a/packages/tailwindcss/src/intellisense.ts
+++ b/packages/tailwindcss/src/intellisense.ts
@@ -55,6 +55,9 @@ export function getClassList(design: DesignSystem): ClassEntry[] {
           item.fraction ||= fraction
           item.modifiers.push(...group.modifiers)
         }
+
+        // Deduplicate modifiers
+        item.modifiers = Array.from(new Set(item.modifiers))
       }
     }
   }
diff --git a/packages/tailwindcss/src/utilities.ts b/packages/tailwindcss/src/utilities.ts
index fa97dbd5273a..9a6906bbd6eb 100644
--- a/packages/tailwindcss/src/utilities.ts
+++ b/packages/tailwindcss/src/utilities.ts
@@ -124,9 +124,12 @@ export class Utilities {
   }
 
   suggest(name: string, groups: () => SuggestionGroup[]) {
-    // TODO: We are calling this multiple times on purpose but ideally only ever
-    // once per utility root.
-    this.completions.set(name, groups)
+    let existingGroups = this.completions.get(name)
+    if (existingGroups) {
+      this.completions.set(name, () => [...existingGroups?.(), ...groups?.()])
+    } else {
+      this.completions.set(name, groups)
+    }
   }
 
   keys(kind: 'static' | 'functional') {