diff --git a/src/app/Flash.jsx b/src/app/Flash.jsx
index 33e66bc..05d191d 100644
--- a/src/app/Flash.jsx
+++ b/src/app/Flash.jsx
@@ -105,6 +105,10 @@ const errors = {
     description: 'Your system does not meet the requirements to flash your device. Make sure to use a browser which ' +
       'supports WebUSB and is up to date.',
   },
+  [Error.STORAGE_SPACE]: {
+    description: 'Your system does not have enough space available to download the system image. Your browser may ' +
+      'be restricting the available space if you are in a private, incognito or guest session.',
+  },
 }
 
 if (isLinux) {
@@ -206,6 +210,7 @@ export default function Flash() {
 
   // Handle user clicking the start button
   const handleStart = () => qdlManager.current?.start()
+  const canStart = step === Step.READY && !error
 
   // Handle retry on error
   const handleRetry = () => window.location.reload()
@@ -222,6 +227,8 @@ export default function Flash() {
     if (progress >= 0) {
       title += ` (${(progress * 100).toFixed(0)}%)`
     }
+  } else if (error === Error.STORAGE_SPACE) {
+    title = message
   } else {
     title = status
   }
@@ -237,8 +244,8 @@ export default function Flash() {
     <div id="flash" className="relative flex flex-col gap-8 justify-center items-center h-full">
       <div
         className={`p-8 rounded-full ${bgColor}`}
-        style={{ cursor: step === Step.READY ? 'pointer' : 'default' }}
-        onClick={step === Step.READY ? handleStart : null}
+        style={{ cursor: canStart ? 'pointer' : 'default' }}
+        onClick={canStart ? handleStart : null}
       >
         <img
           src={icon}
diff --git a/src/utils/manifest.test.js b/src/utils/manifest.test.js
index 8fc87de..617bea3 100644
--- a/src/utils/manifest.test.js
+++ b/src/utils/manifest.test.js
@@ -7,6 +7,7 @@ import { getManifest } from './manifest'
 
 globalThis.navigator = {
   storage: {
+    estimate: vi.fn().mockImplementation(() => ({ quota: 10 * (1024 ** 3) })),
     getDirectory: () => ({
       getFileHandle: () => ({
         createWritable: vi.fn().mockImplementation(() => ({
diff --git a/src/utils/qdl.js b/src/utils/qdl.js
index a151f67..509bd4b 100644
--- a/src/utils/qdl.js
+++ b/src/utils/qdl.js
@@ -25,6 +25,7 @@ export const Error = {
   FLASH_FAILED: 6,
   ERASE_FAILED: 7,
   REQUIREMENTS_NOT_MET: 8,
+  STORAGE_SPACE: 9,
 }
 
 /**
@@ -170,7 +171,12 @@ export class QdlManager {
       this.setStep(Step.READY)
     } catch (err) {
       console.error('[QDL] Initialization error', err)
-      this.setError(Error.UNKNOWN)
+      if (err.startsWith('Not enough storage')) {
+        this.setError(Error.STORAGE_SPACE)
+        this.setMessage(err)
+      } else {
+        this.setError(Error.UNKNOWN)
+      }
     }
   }
 
diff --git a/src/workers/image.worker.js b/src/workers/image.worker.js
index a9b1d82..bfb4df1 100644
--- a/src/workers/image.worker.js
+++ b/src/workers/image.worker.js
@@ -39,6 +39,8 @@ async function readChunks(reader, total, { onChunk, onProgress = undefined }) {
   }
 }
 
+const MIN_QUOTA_MB = 5250
+
 /** @type {FileSystemDirectoryHandle} */
 let root
 
@@ -48,15 +50,17 @@ let root
 
 const imageWorker = {
   async init() {
-    if (root) {
-      console.warn('[ImageWorker] Already initialized')
-      return
+    if (!root) {
+      root = await navigator.storage.getDirectory()
+      await root.remove({ recursive: true })
+      console.info('[ImageWorker] Initialized')
     }
 
-    // TODO: check storage quota and report error if insufficient
-    root = await navigator.storage.getDirectory()
-    await root.remove({ recursive: true })
-    console.info('[ImageWorker] Initialized')
+    const estimate = await navigator.storage.estimate()
+    const quotaMB = (estimate.quota || 0) / (1024 ** 2)
+    if (quotaMB < MIN_QUOTA_MB) {
+      throw `Not enough storage: ${quotaMB.toFixed(0)}MB free, need ${MIN_QUOTA_MB.toFixed(0)}MB`
+    }
   },
 
   /**