diff --git a/src/context.ts b/src/context.ts
index bdac8988..c86c3ef1 100644
--- a/src/context.ts
+++ b/src/context.ts
@@ -26,10 +26,12 @@ export class NuxtIconModuleContext {
   public scanner: IconUsageScanner | undefined
 
   getRuntimeCollections(runtimeOptions: NuxtIconRuntimeOptions): string[] {
+    // Copy: the custom prefixes below are appended in place, and `collectionNames`
+    // is a module-level constant shared with every other consumer in the process
     const resolved = runtimeOptions.fallbackToApi
-      ? collectionNames
+      ? [...collectionNames]
       : typeof this.options.serverBundle === 'string'
-        ? collectionNames
+        ? [...collectionNames]
         : this.options.serverBundle
           ? this.options.serverBundle.collections
             ?.map(c => typeof c === 'string' ? c : c.prefix) || []
diff --git a/test/runtime-collections.test.ts b/test/runtime-collections.test.ts
new file mode 100644
index 00000000..4bd9750f
--- /dev/null
+++ b/test/runtime-collections.test.ts
@@ -0,0 +1,51 @@
+import { expect, it } from 'vitest'
+import type { Nuxt } from '@nuxt/schema'
+import type { IconifyJSON } from '@iconify/types'
+import { NuxtIconModuleContext } from '../src/context'
+import type { ModuleOptions, NuxtIconRuntimeOptions } from '../src/types'
+import { collectionNames } from '../src/collection-names'
+
+function createContext(options: Partial<ModuleOptions>) {
+  const nuxt = {
+    options: {
+      rootDir: '/root',
+      nitro: {},
+      dev: false,
+    },
+  }
+  return new NuxtIconModuleContext(nuxt as unknown as Nuxt, options as ModuleOptions)
+}
+
+// `module.ts` only reads `fallbackToApi` out of the runtime options here
+const runtimeOptions = { fallbackToApi: true } as NuxtIconRuntimeOptions
+
+const customCollection: IconifyJSON = {
+  prefix: 'my-icons',
+  icons: {
+    logo: { body: '<path d="M0 0h24v24H0z"/>' },
+  },
+}
+
+it('keeps custom collection prefixes out of the shared Iconify collection list', () => {
+  const ctx = createContext({ customCollections: [customCollection] })
+  expect(ctx.getRuntimeCollections(runtimeOptions)).toContain('my-icons')
+
+  // Another app built in the same process must not inherit the first one's prefixes
+  const other = createContext({})
+  expect(other.getRuntimeCollections(runtimeOptions)).not.toContain('my-icons')
+  expect(collectionNames).not.toContain('my-icons')
+})
+
+it('does not add a remote endpoint for a custom collection', async () => {
+  const ctx = createContext({
+    provider: 'server',
+    serverBundle: 'remote',
+    customCollections: [customCollection],
+  })
+  // `module.ts` fills `appConfig.icon.collections` from this before the server bundle resolves
+  ctx.getRuntimeCollections(runtimeOptions)
+
+  const { collections } = await ctx.resolveServerBundle()
+  const entries = collections.filter(c => (typeof c === 'string' ? c : c.prefix) === 'my-icons')
+  expect(entries).toEqual([customCollection])
+})