diff --git a/src/frontend/src/features/rooms/livekit/components/ScreenShareFullscreenButton.tsx b/src/frontend/src/features/rooms/livekit/components/ScreenShareFullscreenButton.tsx
new file mode 100644
index 00000000..6718eada
--- /dev/null
+++ b/src/frontend/src/features/rooms/livekit/components/ScreenShareFullscreenButton.tsx
@@ -0,0 +1,76 @@
+import { Button } from '@/primitives'
+import { RiCollapseDiagonalLine, RiExpandDiagonalLine } from '@remixicon/react'
+import { memo, useCallback, useEffect, useRef, useState } from 'react'
+import { useTranslation } from 'react-i18next'
+import { useScreenReaderAnnounce } from '@/hooks/useScreenReaderAnnounce'
+
+// Keeps the fullscreen state here rather than on the toolbar, so entering or
+// leaving fullscreen does not re-render the zoom controls.
+export const ScreenShareFullscreenButton = memo(
+  ({
+    containerRef,
+  }: {
+    containerRef: React.RefObject<HTMLDivElement | null>
+  }) => {
+    const { t } = useTranslation('rooms', { keyPrefix: 'screenShareZoom' })
+    const announce = useScreenReaderAnnounce()
+
+    const [isFullscreen, setIsFullscreen] = useState(false)
+    // Tracks whether this tile's container triggered fullscreen (vs another share's).
+    const wasThisTileFullscreen = useRef(false)
+
+    // Covers Esc and browser UI exits, not just this button.
+    // Only this tile's instance announces to avoid duplicates with multiple shares.
+    useEffect(() => {
+      const onChange = () => {
+        const isThisTileFullscreen =
+          document.fullscreenElement === containerRef.current
+        setIsFullscreen(isThisTileFullscreen)
+
+        if (isThisTileFullscreen) {
+          wasThisTileFullscreen.current = true
+          announce(t('fullScreenEntered'), 'assertive')
+        } else if (wasThisTileFullscreen.current) {
+          wasThisTileFullscreen.current = false
+          announce(t('fullScreenExited'), 'assertive')
+        }
+      }
+      document.addEventListener('fullscreenchange', onChange)
+      return () => document.removeEventListener('fullscreenchange', onChange)
+    }, [announce, t, containerRef])
+
+    const toggleFullScreen = useCallback(async () => {
+      try {
+        if (document.fullscreenElement === containerRef.current) {
+          await document.exitFullscreen()
+        } else {
+          // Tile container so zoom controls stay visible in fullscreen.
+          await containerRef.current?.requestFullscreen()
+        }
+      } catch (error) {
+        console.error('Error toggling fullscreen:', error)
+      }
+    }, [containerRef])
+
+    if (!document.fullscreenEnabled) return null
+
+    return (
+      <Button
+        size="sm"
+        variant="primaryTextDark"
+        square
+        tooltip={isFullscreen ? t('exitFullScreen') : t('fullScreen')}
+        aria-label={isFullscreen ? t('exitFullScreen') : t('fullScreen')}
+        onPress={toggleFullScreen}
+      >
+        {isFullscreen ? (
+          <RiCollapseDiagonalLine size={20} />
+        ) : (
+          <RiExpandDiagonalLine size={20} />
+        )}
+      </Button>
+    )
+  }
+)
+
+ScreenShareFullscreenButton.displayName = 'ScreenShareFullscreenButton'
diff --git a/src/frontend/src/features/rooms/livekit/components/ScreenShareZoomControls.tsx b/src/frontend/src/features/rooms/livekit/components/ScreenShareZoomControls.tsx
index b0dcfa41..53c14213 100644
--- a/src/frontend/src/features/rooms/livekit/components/ScreenShareZoomControls.tsx
+++ b/src/frontend/src/features/rooms/livekit/components/ScreenShareZoomControls.tsx
@@ -3,13 +3,11 @@ import { HStack } from '@/styled-system/jsx'
 import { Button } from '@/primitives'
 import {
   RiFullscreenExitLine,
-  RiFullscreenLine,
   RiZoomInLine,
   RiZoomOutLine,
 } from '@remixicon/react'
 import { useTranslation } from 'react-i18next'
-import { useCallback, useEffect, useRef, useState } from 'react'
-import { useScreenReaderAnnounce } from '@/hooks/useScreenReaderAnnounce'
+import { ScreenShareFullscreenButton } from './ScreenShareFullscreenButton'
 
 interface ScreenShareZoomControlsProps {
   containerRef: React.RefObject<HTMLDivElement | null>
@@ -33,46 +31,6 @@ export const ScreenShareZoomControls = ({
   onResetZoom,
 }: ScreenShareZoomControlsProps) => {
   const { t } = useTranslation('rooms', { keyPrefix: 'screenShareZoom' })
-  const announce = useScreenReaderAnnounce()
-
-  const [isFullscreen, setIsFullscreen] = useState(false)
-  const wasOwnFullscreen = useRef(false)
-  const [isFullscreenAvailable] = useState(
-    () => typeof document !== 'undefined' && document.fullscreenEnabled
-  )
-
-  // Covers Esc and browser UI exits, not just the toolbar button.
-  // Only this tile's instance announces to avoid duplicates with multiple shares.
-  useEffect(() => {
-    const onChange = () => {
-      const isThisTileFullscreen =
-        document.fullscreenElement === containerRef.current
-      setIsFullscreen(isThisTileFullscreen)
-
-      if (isThisTileFullscreen) {
-        wasOwnFullscreen.current = true
-        announce(t('fullScreenEntered'), 'assertive')
-      } else if (wasOwnFullscreen.current) {
-        wasOwnFullscreen.current = false
-        announce(t('fullScreenExited'), 'assertive')
-      }
-    }
-    document.addEventListener('fullscreenchange', onChange)
-    return () => document.removeEventListener('fullscreenchange', onChange)
-  }, [announce, t, containerRef])
-
-  const toggleFullScreen = useCallback(async () => {
-    try {
-      if (document.fullscreenElement === containerRef.current) {
-        await document.exitFullscreen()
-      } else {
-        // Tile container so zoom controls stay visible in fullscreen.
-        await containerRef.current?.requestFullscreen()
-      }
-    } catch (error) {
-      console.error('Error toggling fullscreen:', error)
-    }
-  }, [containerRef])
 
   return (
     <div
@@ -153,22 +111,7 @@ export const ScreenShareZoomControls = ({
         >
           <RiZoomInLine size={18} />
         </Button>
-        {isFullscreenAvailable && (
-          <Button
-            size="sm"
-            variant="primaryTextDark"
-            square
-            tooltip={isFullscreen ? t('exitFullScreen') : t('fullScreen')}
-            aria-label={isFullscreen ? t('exitFullScreen') : t('fullScreen')}
-            onPress={toggleFullScreen}
-          >
-            {isFullscreen ? (
-              <RiFullscreenExitLine size={18} />
-            ) : (
-              <RiFullscreenLine size={18} />
-            )}
-          </Button>
-        )}
+        <ScreenShareFullscreenButton containerRef={containerRef} />
       </HStack>
     </div>
   )