diff --git a/ElectronClient/gui/editors/TinyMCE.tsx b/ElectronClient/gui/editors/TinyMCE.tsx
index b30eac8497..82524d039f 100644
--- a/ElectronClient/gui/editors/TinyMCE.tsx
+++ b/ElectronClient/gui/editors/TinyMCE.tsx
@@ -55,9 +55,10 @@ function findBlockSource(node:any) {
 
 function newBlockSource(language:string = '', content:string = ''):any {
 	const fence = language === 'katex' ? '$$' : '```';
+	const fenceLanguage = language === 'katex' ? '' : language;
 
 	return {
-		openCharacters: `\n${fence}${language}\n`,
+		openCharacters: `\n${fence}${fenceLanguage}\n`,
 		closeCharacters: `\n${fence}\n`,
 		content: content,
 		node: null,
diff --git a/ReactNativeClient/lib/joplin-renderer/MdToHtml/rules/katex.js b/ReactNativeClient/lib/joplin-renderer/MdToHtml/rules/katex.js
index c2252d2997..ba9164f073 100644
--- a/ReactNativeClient/lib/joplin-renderer/MdToHtml/rules/katex.js
+++ b/ReactNativeClient/lib/joplin-renderer/MdToHtml/rules/katex.js
@@ -230,7 +230,7 @@ module.exports = {
 			const katexInline = function(latex) {
 				options.displayMode = false;
 				try {
-					return `<span class="joplin-editable"><span class="joplin-source" data-joplin-language="katex" data-joplin-source-open="$" data-joplin-source-close="$">${latex}</span>${renderToStringWithCache(latex, options)}</span>`;
+					return `<span class="joplin-editable"><span class="joplin-source" data-joplin-language="katex" data-joplin-source-open="$" data-joplin-source-close="$">${md.utils.escapeHtml(latex)}</span>${renderToStringWithCache(latex, options)}</span>`;
 				} catch (error) {
 					console.error('Katex error for:', latex, error);
 					return latex;
@@ -245,7 +245,7 @@ module.exports = {
 			const katexBlock = function(latex) {
 				options.displayMode = true;
 				try {
-					return `<div class="joplin-editable"><pre class="joplin-source" data-joplin-language="katex" data-joplin-source-open="$$&#10;" data-joplin-source-close="&#10;$$&#10;">${latex}</pre>${renderToStringWithCache(latex, options)}</div>`;
+					return `<div class="joplin-editable"><pre class="joplin-source" data-joplin-language="katex" data-joplin-source-open="$$&#10;" data-joplin-source-close="&#10;$$&#10;">${md.utils.escapeHtml(latex)}</pre>${renderToStringWithCache(latex, options)}</div>`;
 				} catch (error) {
 					console.error('Katex error for:', latex, error);
 					return latex;