diff --git a/dev/Common/Utils.js b/dev/Common/Utils.js
index f1eb99dba..ed395fbd7 100644
--- a/dev/Common/Utils.js
+++ b/dev/Common/Utils.js
@@ -49,6 +49,15 @@ export const
 		}
 	},
 
+	// unescape(encodeURIComponent()) makes the UTF-16 DOMString to an UTF-8 string
+	b64EncodeJSON = data => btoa(unescape(encodeURIComponent(JSON.stringify(data)))),
+/* 	// Without deprecated 'unescape':
+	b64EncodeJSON = data => btoa(encodeURIComponent(JSON.stringify(data)).replace(
+		/%([0-9A-F]{2})/g, (match, p1) => String.fromCharCode('0x' + p1)
+    )),
+*/
+	b64EncodeJSONSafe = data => b64EncodeJSON(data).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, ''),
+
 	settingsSaveHelperSimpleFunction = (koTrigger, context) =>
 		iError => {
 			koTrigger.call(context, iError ? SaveSettingsStep.FalseResult : SaveSettingsStep.TrueResult);
diff --git a/dev/Model/SieveScript.js b/dev/Model/SieveScript.js
index 18b4eb02c..620abfe86 100644
--- a/dev/Model/SieveScript.js
+++ b/dev/Model/SieveScript.js
@@ -2,7 +2,7 @@ import ko from 'ko';
 
 import { AbstractModel } from 'Knoin/AbstractModel';
 import { FilterModel } from 'Model/Filter';
-import { arrayLength, pString } from 'Common/Utils';
+import { arrayLength, pString, b64EncodeJSON } from 'Common/Utils';
 
 const SIEVE_FILE_NAME = 'rainloop.user';
 
@@ -215,7 +215,7 @@ function filtersToSieveScript(filters)
 			'/*',
 			'BEGIN:FILTER:' + filter.id,
 			'BEGIN:HEADER',
-			btoa(unescape(encodeURIComponent(JSON.stringify(filter.toJson())))).match(split).join(eol) + 'END:HEADER',
+			b64EncodeJSON(filter.toJson()).match(split).join(eol) + 'END:HEADER',
 			'*/',
 			filter.enabled() ? '' : '/* @Filter is disabled ',
 			filterToString(filter, require),