diff --git a/core/js/src/datepicker.ts b/core/js/src/datepicker.ts
index f25b040b3..750e8ee55 100644
--- a/core/js/src/datepicker.ts
+++ b/core/js/src/datepicker.ts
@@ -43,6 +43,8 @@ const DATE_PATTERN = /^(\d{4})-(\d{2})-(\d{2})$/
 // Vanilla Calendar Pro 3.4+ throws on an option whose extension is not registered
 const PLUGIN_EXTENSIONS = ['annotations', 'months', 'motion', 'time', 'weeks'] as const
 
+type ExtensionOptions = { extensions?: object[] }
+
 // The public API is typed with local copies of the Vanilla Calendar Pro types.
 // `vanilla-calendar-pro` is an optional peer dependency, so the published
 // `dist/types` must not import it: a project that never loads the datepicker
@@ -559,12 +561,12 @@ class Datepicker extends BaseComponent {
   }
 
   /** @internal */
-  _buildCalendarOptions(): Options {
+  _buildCalendarOptions(): Options & ExtensionOptions {
     // The plugin uses 'system' for auto-detection, Bootstrap and Tabler use 'auto'
     const theme = this._getEffectiveTheme()
     const vcpTheme = !theme || theme === 'auto' ? 'system' : theme
 
-    const calendarOptions: Options = {
+    const calendarOptions: Options & ExtensionOptions = {
       ...this._config.vcpOptions,
       inputMode: !this._isInline,
       positionToInput: this._config.placement,
@@ -610,11 +612,12 @@ class Datepicker extends BaseComponent {
   }
 
   /** @internal */
-  _getPluginExtensions(): NonNullable<Options['extensions']> {
-    const extensions = [...((this._config.vcpOptions as Options).extensions ?? [])]
+  _getPluginExtensions(): object[] {
+    const extensions = [...((this._config.vcpOptions as ExtensionOptions).extensions ?? [])]
+    const plugin = window.VanillaCalendarPro as Record<string, unknown> | undefined
 
     for (const name of PLUGIN_EXTENSIONS) {
-      const extension = window.VanillaCalendarPro?.[name]
+      const extension = plugin?.[name]
       if (extension && !extensions.includes(extension)) {
         extensions.push(extension)
       }
diff --git a/core/js/tests/unit/datepicker.spec.ts b/core/js/tests/unit/datepicker.spec.ts
index bf0ad5414..2544aa22c 100644
--- a/core/js/tests/unit/datepicker.spec.ts
+++ b/core/js/tests/unit/datepicker.spec.ts
@@ -154,13 +154,24 @@ describe('Datepicker', () => {
       expect(fixtureEl.querySelector('[data-vc="time"]')).not.toBeNull()
     })
 
-    it('should keep extensions passed through vcpOptions', () => {
+    it('should register the plugin extensions and keep those passed through vcpOptions', () => {
+      const months = { name: 'months' }
+      const custom = { name: 'custom' }
+      window.VanillaCalendarPro = { ...VanillaCalendarPro, months } as unknown as typeof VanillaCalendarPro
       fixtureEl.innerHTML = '<input type="text" data-bs-toggle="datepicker">'
 
-      const instance = new Datepicker(input(), { vcpOptions: { extensions: [VanillaCalendarPro.time] } })
+      const instance = new Datepicker(input(), { vcpOptions: { extensions: [custom, months] } })
 
-      expect(instance.calendar!.extensions).toContain(VanillaCalendarPro.time)
-      expect(instance.calendar!.extensions).toContain(VanillaCalendarPro.months)
+      expect(instance._buildCalendarOptions().extensions).toEqual([custom, months])
+    })
+
+    it('should not pass extensions when the plugin has none', () => {
+      window.VanillaCalendarPro = { Calendar: VanillaCalendarPro.Calendar } as unknown as typeof VanillaCalendarPro
+      fixtureEl.innerHTML = '<input type="text" data-bs-toggle="datepicker">'
+
+      const instance = new Datepicker(input())
+
+      expect(instance._buildCalendarOptions()).not.toHaveProperty('extensions')
     })
   })
 
diff --git a/core/package.json b/core/package.json
index e1a5a4d75..8add9cc8e 100644
--- a/core/package.json
+++ b/core/package.json
@@ -287,7 +287,7 @@
     "tom-select": "^2.6.2",
     "typed.js": "^3.0.0",
     "typescript": "^7.0.2",
-    "vanilla-calendar-pro": "^3.4.0",
+    "vanilla-calendar-pro": "^3.3.2",
     "vitest": "4.1.11"
   }
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 0d91c2786..f5d87b3c0 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -214,8 +214,8 @@ importers:
         specifier: ^7.0.2
         version: 7.0.2
       vanilla-calendar-pro:
-        specifier: ^3.4.0
-        version: 3.4.0
+        specifier: ^3.3.2
+        version: 3.3.2
       vitest:
         specifier: 4.1.11
         version: 4.1.11(@types/node@26.4.0)(@vitest/browser-playwright@4.1.11)(@vitest/coverage-istanbul@4.1.11)(esbuild@0.28.1)(sass@1.103.1)(terser@5.51.2)(tsx@4.23.13)(yaml@2.9.0)
@@ -4601,8 +4601,8 @@ packages:
   validate-npm-package-license@3.0.4:
     resolution: {integrity: sha512-DpKm2Ui/xN7/HQKCtpZxoRWBhZ9Z0kqtygG8XCgNQ8ZlDnxuQmWhj566j8fN4Cu3/JmbhsDo7fcAJq4s9h27Ew==}
 
-  vanilla-calendar-pro@3.4.0:
-    resolution: {integrity: sha512-HLWjzHOWvMIrjI77tXK5bYzp0s5TeBSrZC247STjcTAdWI7kqEwWT6Xvu20vqdwzF498H1Da8l4WpdgVIGtc1Q==}
+  vanilla-calendar-pro@3.3.2:
+    resolution: {integrity: sha512-RaLpDtvQFeKi0ajOpGBedLNrr0YoiYAF+0sppk4XZV/U57AuihJIhw8h2whUvIG1ZSR3LrdSXk3lHLkCPGlHvg==}
 
   vfile-location@5.0.3:
     resolution: {integrity: sha512-5yXvWDEgqeiYiBe1lbxYF7UMAIm/IcopxMHrMQDq3nvKcjPKIhZklUKL+AE7J7uApI4kwe2snsK+eI6UTj9EHg==}
@@ -9590,7 +9590,7 @@ snapshots:
       spdx-correct: 3.2.0
       spdx-expression-parse: 3.0.1
 
-  vanilla-calendar-pro@3.4.0: {}
+  vanilla-calendar-pro@3.3.2: {}
 
   vfile-location@5.0.3:
     dependencies: