diff --git a/lib/gui/etcher.ts b/lib/gui/etcher.ts
index 76cf50b5..afb7842a 100644
--- a/lib/gui/etcher.ts
+++ b/lib/gui/etcher.ts
@@ -17,6 +17,7 @@
 import { delay } from 'bluebird';
 import * as electron from 'electron';
 import { autoUpdater } from 'electron-updater';
+import { promises as fs } from 'fs';
 import { platform } from 'os';
 import * as _ from 'lodash';
 import * as path from 'path';
@@ -57,7 +58,17 @@ async function checkForUpdates(interval: number) {
 	}
 }
 
-function getCommandLineURL(argv: string[]): string | undefined {
+async function isFile(filePath: string): Promise<boolean> {
+	try {
+		const stat = await fs.stat(filePath);
+		return stat.isFile();
+	} catch {
+		// noop
+	}
+	return false;
+}
+
+async function getCommandLineURL(argv: string[]): Promise<string | undefined> {
 	argv = argv.slice(electron.app.isPackaged ? 1 : 2);
 	if (argv.length) {
 		const value = argv[argv.length - 1];
@@ -69,6 +80,14 @@ function getCommandLineURL(argv: string[]): string | undefined {
 		if (platform() === 'darwin' && value.startsWith('-psn_')) {
 			return;
 		}
+		if (
+			!value.startsWith('http://') &&
+			!value.startsWith('https://') &&
+			!value.startsWith(scheme) &&
+			!(await isFile(value))
+		) {
+			return;
+		}
 		return value;
 	}
 }
@@ -204,9 +223,9 @@ async function main(): Promise<void> {
 				window.restore();
 			}
 			window.focus();
-			await selectImageURL(getCommandLineURL(argv));
+			await selectImageURL(await getCommandLineURL(argv));
 		});
-		await selectImageURL(getCommandLineURL(process.argv));
+		await selectImageURL(await getCommandLineURL(process.argv));
 	}
 }
 
diff --git a/lib/gui/modules/child-writer.ts b/lib/gui/modules/child-writer.ts
index 108932e8..4cd5e2f9 100644
--- a/lib/gui/modules/child-writer.ts
+++ b/lib/gui/modules/child-writer.ts
@@ -119,7 +119,7 @@ async function writeAndValidate({
 		onProgress,
 		verify,
 		trim: autoBlockmapping,
-		numBuffers: 32,
+		numBuffers: Math.min(2 + (destinations.length - 1) * 32, 256),
 		decompressFirst,
 	});
 	const result: WriteResult = {
diff --git a/npm-shrinkwrap.json b/npm-shrinkwrap.json
index a970382b..d817f6a6 100644
--- a/npm-shrinkwrap.json
+++ b/npm-shrinkwrap.json
@@ -5355,9 +5355,9 @@
       "dev": true
     },
     "etcher-sdk": {
-      "version": "4.1.8",
-      "resolved": "https://registry.npmjs.org/etcher-sdk/-/etcher-sdk-4.1.8.tgz",
-      "integrity": "sha512-fSNwpqeCdc75xNIKwf+At8+r/EQ+/X/IV7gUYFa/wKXtnFHHxYJor6VfPdELUbtDDBWWa2cneJvtwGmcDPBAvA==",
+      "version": "4.1.13",
+      "resolved": "https://registry.npmjs.org/etcher-sdk/-/etcher-sdk-4.1.13.tgz",
+      "integrity": "sha512-ITzBgoy8AGI6/DHyS43wix2TNa9kVeILsr/vQl75Hbbt5gM4C2ygwqABG7V+MGTaNphWc2OstSP9k6xQpGfttw==",
       "dev": true,
       "requires": {
         "@ronomon/direct-io": "^3.0.1",
@@ -15060,4 +15060,4 @@
       }
     }
   }
-}
+}
\ No newline at end of file
diff --git a/package.json b/package.json
index 61e2bfd7..a62a862d 100644
--- a/package.json
+++ b/package.json
@@ -77,7 +77,7 @@
     "electron-notarize": "^0.3.0",
     "electron-rebuild": "^1.11.0",
     "electron-updater": "^4.3.2",
-    "etcher-sdk": "^4.1.8",
+    "etcher-sdk": "^4.1.13",
     "file-loader": "^6.0.0",
     "flexboxgrid": "^6.3.0",
     "husky": "^4.2.5",