diff --git a/packages/@headlessui-react/CHANGELOG.md b/packages/@headlessui-react/CHANGELOG.md
index aaa769a..0c748df 100644
--- a/packages/@headlessui-react/CHANGELOG.md
+++ b/packages/@headlessui-react/CHANGELOG.md
@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `by` prop for `Listbox`, `Combobox` and `RadioGroup` ([#1482](https://github.com/tailwindlabs/headlessui/pull/1482))
 - Add `@headlessui/tailwindcss` plugin ([#1487](https://github.com/tailwindlabs/headlessui/pull/1487))
 
+### Fixed
+
+- Fixed SSR support on Deno ([#1671](https://github.com/tailwindlabs/headlessui/pull/1671))
+
 ## [1.6.6] - 2022-07-07
 
 ### Fixed
diff --git a/packages/@headlessui-react/src/components/portal/portal.tsx b/packages/@headlessui-react/src/components/portal/portal.tsx
index 86bdba1..614a80a 100644
--- a/packages/@headlessui-react/src/components/portal/portal.tsx
+++ b/packages/@headlessui-react/src/components/portal/portal.tsx
@@ -21,6 +21,7 @@ import { useServerHandoffComplete } from '../../hooks/use-server-handoff-complet
 import { optionalRef, useSyncRefs } from '../../hooks/use-sync-refs'
 import { useOwnerDocument } from '../../hooks/use-owner'
 import { microTask } from '../../utils/micro-task'
+import { isServer } from '../../utils/ssr'
 
 function usePortalTarget(ref: MutableRefObject<HTMLElement | null>): HTMLElement | null {
   let forceInRoot = usePortalRoot()
@@ -33,7 +34,7 @@ function usePortalTarget(ref: MutableRefObject<HTMLElement | null>): HTMLElement
     if (!forceInRoot && groupTarget !== null) return null
 
     // No group context is used, let's create a default portal root
-    if (typeof window === 'undefined') return null
+    if (isServer) return null
     let existingRoot = ownerDocument?.getElementById('headlessui-portal-root')
     if (existingRoot) return existingRoot
 
@@ -81,7 +82,7 @@ let PortalRoot = forwardRefWithAs(function Portal<
   let ownerDocument = useOwnerDocument(internalPortalRootRef)
   let target = usePortalTarget(internalPortalRootRef)
   let [element] = useState<HTMLDivElement | null>(() =>
-    typeof window === 'undefined' ? null : ownerDocument?.createElement('div') ?? null
+    isServer ? null : ownerDocument?.createElement('div') ?? null
   )
 
   let ready = useServerHandoffComplete()
diff --git a/packages/@headlessui-react/src/hooks/use-iso-morphic-effect.ts b/packages/@headlessui-react/src/hooks/use-iso-morphic-effect.ts
index 7c7eae2..79a2219 100644
--- a/packages/@headlessui-react/src/hooks/use-iso-morphic-effect.ts
+++ b/packages/@headlessui-react/src/hooks/use-iso-morphic-effect.ts
@@ -1,3 +1,4 @@
 import { useLayoutEffect, useEffect } from 'react'
+import { isServer } from '../utils/ssr'
 
-export let useIsoMorphicEffect = typeof window !== 'undefined' ? useLayoutEffect : useEffect
+export let useIsoMorphicEffect = isServer ? useEffect : useLayoutEffect
diff --git a/packages/@headlessui-react/src/utils/owner.ts b/packages/@headlessui-react/src/utils/owner.ts
index 296975e..5bbc186 100644
--- a/packages/@headlessui-react/src/utils/owner.ts
+++ b/packages/@headlessui-react/src/utils/owner.ts
@@ -1,9 +1,10 @@
 import { MutableRefObject } from 'react'
+import { isServer } from './ssr'
 
 export function getOwnerDocument<T extends Element | MutableRefObject<Element | null>>(
   element: T | null | undefined
 ) {
-  if (typeof window === 'undefined') return null
+  if (isServer) return null
   if (element instanceof Node) return element.ownerDocument
   if (element?.hasOwnProperty('current')) {
     if (element.current instanceof Node) return element.current.ownerDocument
diff --git a/packages/@headlessui-react/src/utils/ssr.ts b/packages/@headlessui-react/src/utils/ssr.ts
new file mode 100644
index 0000000..5df1767
--- /dev/null
+++ b/packages/@headlessui-react/src/utils/ssr.ts
@@ -0,0 +1 @@
+export const isServer = typeof window === 'undefined' || typeof document === 'undefined'
diff --git a/packages/@headlessui-vue/CHANGELOG.md b/packages/@headlessui-vue/CHANGELOG.md
index dfcf8ba..7638e9d 100644
--- a/packages/@headlessui-vue/CHANGELOG.md
+++ b/packages/@headlessui-vue/CHANGELOG.md
@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `by` prop for `Listbox`, `Combobox` and `RadioGroup` ([#1482](https://github.com/tailwindlabs/headlessui/pull/1482))
 - Add `@headlessui/tailwindcss` plugin ([#1487](https://github.com/tailwindlabs/headlessui/pull/1487))
 
+### Fixed
+
+- Fixed SSR support on Deno ([#1671](https://github.com/tailwindlabs/headlessui/pull/1671))
+
 ## [1.6.7] - 2022-07-12
 
 ### Fixed
diff --git a/packages/@headlessui-vue/src/components/focus-trap/focus-trap.test.ts b/packages/@headlessui-vue/src/components/focus-trap/focus-trap.test.ts
index 16ed5f3..8ae1d20 100644
--- a/packages/@headlessui-vue/src/components/focus-trap/focus-trap.test.ts
+++ b/packages/@headlessui-vue/src/components/focus-trap/focus-trap.test.ts
@@ -1,4 +1,4 @@
-import { ref, nextTick, onMounted } from 'vue'
+import { ref, onMounted } from 'vue'
 
 import { FocusTrap } from './focus-trap'
 import { assertActiveElement, getByText } from '../../test-utils/accessibility-assertions'
diff --git a/packages/@headlessui-vue/src/hooks/use-event-listener.ts b/packages/@headlessui-vue/src/hooks/use-event-listener.ts
index 7f761a3..07a507e 100644
--- a/packages/@headlessui-vue/src/hooks/use-event-listener.ts
+++ b/packages/@headlessui-vue/src/hooks/use-event-listener.ts
@@ -1,4 +1,5 @@
 import { watchEffect } from 'vue'
+import { isServer } from '../utils/ssr'
 
 export function useEventListener<TType extends keyof WindowEventMap>(
   element: HTMLElement | Document | Window | EventTarget | null | undefined,
@@ -6,7 +7,7 @@ export function useEventListener<TType extends keyof WindowEventMap>(
   listener: (event: WindowEventMap[TType]) => any,
   options?: boolean | AddEventListenerOptions
 ) {
-  if (typeof window === 'undefined') return
+  if (isServer) return
 
   watchEffect((onInvalidate) => {
     element = element ?? window
diff --git a/packages/@headlessui-vue/src/hooks/use-window-event.ts b/packages/@headlessui-vue/src/hooks/use-window-event.ts
index 5c9f971..267d78b 100644
--- a/packages/@headlessui-vue/src/hooks/use-window-event.ts
+++ b/packages/@headlessui-vue/src/hooks/use-window-event.ts
@@ -1,11 +1,12 @@
 import { watchEffect } from 'vue'
+import { isServer } from '../utils/ssr'
 
 export function useWindowEvent<TType extends keyof WindowEventMap>(
   type: TType,
   listener: (this: Window, ev: WindowEventMap[TType]) => any,
   options?: boolean | AddEventListenerOptions
 ) {
-  if (typeof window === 'undefined') return
+  if (isServer) return
 
   watchEffect((onInvalidate) => {
     window.addEventListener(type, listener, options)
diff --git a/packages/@headlessui-vue/src/utils/owner.ts b/packages/@headlessui-vue/src/utils/owner.ts
index afbe9d7..eebd7c6 100644
--- a/packages/@headlessui-vue/src/utils/owner.ts
+++ b/packages/@headlessui-vue/src/utils/owner.ts
@@ -1,10 +1,11 @@
 import { Ref } from 'vue'
 import { dom } from './dom'
+import { isServer } from './ssr'
 
 export function getOwnerDocument<T extends Element | Ref<Element | null>>(
   element: T | null | undefined
 ) {
-  if (typeof window === 'undefined') return null
+  if (isServer) return null
   if (element instanceof Node) return element.ownerDocument
   if (element?.hasOwnProperty('value')) {
     let domElement = dom(element)
diff --git a/packages/@headlessui-vue/src/utils/ssr.ts b/packages/@headlessui-vue/src/utils/ssr.ts
new file mode 100644
index 0000000..5df1767
--- /dev/null
+++ b/packages/@headlessui-vue/src/utils/ssr.ts
@@ -0,0 +1 @@
+export const isServer = typeof window === 'undefined' || typeof document === 'undefined'
diff --git a/packages/playground-react/pages/combinations/form.tsx b/packages/playground-react/pages/combinations/form.tsx
index 3c8fcb5..99bc2f4 100644
--- a/packages/playground-react/pages/combinations/form.tsx
+++ b/packages/playground-react/pages/combinations/form.tsx
@@ -20,7 +20,9 @@ let people = [
 let locations = ['New York', 'London', 'Paris', 'Berlin']
 
 export default function App() {
-  let [result, setResult] = useState(() => (typeof window === 'undefined' ? [] : new FormData()))
+  let [result, setResult] = useState(() =>
+    typeof window === 'undefined' || typeof document === 'undefined' ? [] : new FormData()
+  )
   let [notifications, setNotifications] = useState(false)
   let [apple, setApple] = useState(false)
   let [banana, setBanana] = useState(false)