diff --git a/src/vs/base/common/strings.ts b/src/vs/base/common/strings.ts
index 06322c3e0b4..e44e219015c 100644
--- a/src/vs/base/common/strings.ts
+++ b/src/vs/base/common/strings.ts
@@ -537,6 +537,27 @@ export function getCharContainingOffset(str: string, offset: number): [number, n
 	return _getCharContainingOffset(str, offset);
 }
 
+/**
+ * Convert a Unicode string to a string in which each 16-bit unit occupies only one byte
+ *
+ * From https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/btoa
+ */
+function toBinary(str: string): string {
+	const codeUnits = new Uint16Array(str.length);
+	for (let i = 0; i < codeUnits.length; i++) {
+		codeUnits[i] = str.charCodeAt(i);
+	}
+	return String.fromCharCode(...new Uint8Array(codeUnits.buffer));
+}
+
+/**
+ * Version of the global `btoa` function that handles multi-byte characters instead
+ * of throwing an exception.
+ */
+export function multibyteAwareBtoa(str: string): string {
+	return btoa(toBinary(str));
+}
+
 /**
  * A manual encoding of `str` to UTF8.
  * Use only in environments which do not offer native conversion methods!
diff --git a/src/vs/workbench/api/browser/mainThreadCustomEditors.ts b/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
index 04aab60a1ad..ff7778c60be 100644
--- a/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
+++ b/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
@@ -11,6 +11,7 @@ import { Disposable, DisposableStore, IDisposable, IReference } from 'vs/base/co
 import { Schemas } from 'vs/base/common/network';
 import { basename } from 'vs/base/common/path';
 import { isEqual, isEqualOrParent, toLocalResource } from 'vs/base/common/resources';
+import { multibyteAwareBtoa } from 'vs/base/common/strings';
 import { URI, UriComponents } from 'vs/base/common/uri';
 import * as modes from 'vs/editor/common/modes';
 import { localize } from 'vs/nls';
@@ -347,7 +348,7 @@ class MainThreadCustomEditorModel extends Disposable implements ICustomEditorMod
 
 	private static toWorkingCopyResource(viewType: string, resource: URI) {
 		const authority = viewType.replace(/[^a-z0-9\-_]/gi, '-');
-		const path = '/' + btoa(resource.with({ query: null, fragment: null }).toString(true));
+		const path = '/' + multibyteAwareBtoa(resource.with({ query: null, fragment: null }).toString(true));
 		return URI.from({
 			scheme: Schemas.vscodeCustomEditor,
 			authority: authority,