diff --git a/src/cli.ts b/src/cli.ts
index 46c7661a..5e48d256 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -93,6 +93,8 @@ const yargs = require('yargs')
 	.default('e', 'utf8')
 	.alias('e', 'encoding')
 	.describe('e', 'Encoding of files/piped data.')
+	// Not .choices() as node takes the name of an encoding in any case, like `UTF8`
+	.check((argv) => Buffer.isEncoding(argv.encoding) || `Unknown encoding: ${argv.encoding}`)
 
 	.alias('E', 'engine')
 	.describe(
diff --git a/src/engine.ts b/src/engine.ts
index 6cb51667..da504e35 100644
--- a/src/engine.ts
+++ b/src/engine.ts
@@ -26,9 +26,16 @@ export {version} from '../package.json';
 const runtime = process.versions.bun ? 'Bun' : 'Node';
 const runtimeEngine = process.versions.bun ? 'JSC' : 'V8';
 
+function validateEncoding(encoding = 'utf8') {
+	if (!Buffer.isEncoding(encoding)) {
+		die('Unknown encoding:', encoding);
+	}
+}
+
 // Returns a promise that resolves when all files are done
 export async function engine(config: any = {engine: 'default'}) {
 	outputConfig(config);
+	validateEncoding(config.encoding);
 
 	step('Displaying steps for:');
 	step(config);
diff --git a/test/cli/run.sh b/test/cli/run.sh
index 3454688c..593f634c 100644
--- a/test/cli/run.sh
+++ b/test/cli/run.sh
@@ -130,6 +130,16 @@ else
 fi
 
 
+# -e
+# An unknown encoding stops the run with an error, both for files and for piped data (#690)
+reset
+assert_failure		"rexreplace o x my.file -e nope"
+assert		 		"cat my.file"    'foobar'
+assert_failure		"printf foo | rexreplace o x -e nope"
+assert		 		"printf foo | rexreplace o x -e nope 2>&1 | grep -v 'exited with code' | tail -1"    'Unknown encoding: nope'
+assert		 		"printf foo | rexreplace o x -e LATIN1"    'fxx'
+
+
 # -b
 reset
 rexreplace o x my.file --keep-backup
diff --git a/test/js/encoding.test.js b/test/js/encoding.test.js
index 8d7d665f..60561781 100644
--- a/test/js/encoding.test.js
+++ b/test/js/encoding.test.js
@@ -49,15 +49,26 @@ describe('--encoding', () => {
 		);
 	});
 
-	test.todo(
-		'BUG #690: an unknown encoding gives an error message instead of crashing',
-		async () => {
-			fs.writeFileSync('my.file', 'foobar');
-			const result = await rr('o', 'x', {includeGlob: ['my.file'], encoding: 'nope'});
-			expect(result.exit).toBe(1);
-			expect(result.err).toContain('nope');
-		}
-	);
+	// The error message, and not the stack trace from deep inside node, when an encoding is unknown (#690)
+	const unknownEncoding = {out: '', err: ' ❌ Unknown encoding: nope\n\n', exit: 1};
+
+	test('stops the run with an error if it is unknown (#690)', async () => {
+		fs.writeFileSync('my.file', 'foobar');
+		expect(await rr('o', 'x', {includeGlob: ['my.file'], encoding: 'nope'})).toEqual(
+			unknownEncoding
+		);
+		expect(fs.readFileSync('my.file', 'utf8')).toBe('foobar');
+	});
+
+	test('stops the run with an error if it is unknown, also for piped data (#690)', async () => {
+		expect(await rr('o', 'x', {pipedData: 'foo', encoding: 'nope'})).toEqual(unknownEncoding);
+	});
+
+	test('is known in any case', async () => {
+		fs.writeFileSync('my.file', latin1());
+		await rr('æ', 'ø', {includeGlob: ['my.file'], encoding: 'LATIN1'});
+		expect(fs.readFileSync('my.file')).toEqual(Buffer.from([0x66, 0xf8, 0x6f]));
+	});
 
 	describe('combined', () => {
 		test.each([