diff --git a/src/parser.js b/src/parser.js
index ae8d152..3bd28e3 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -94,10 +94,12 @@ function getTags(post) {
 }
 
 function processCategoryTags(post, domain) {
+	if (!post.category) {
+		return [];
+	}
 	return post.category
 		.filter(c => c["$"].domain === domain)
-		.map(({ $: c }) => c.nicename)
-		.join(", ");
+		.map(({ $: c }) => c.nicename);
 }
 
 function collectAttachedImages(data) {
diff --git a/src/writer.js b/src/writer.js
index 5bff9c0..88d4e89 100644
--- a/src/writer.js
+++ b/src/writer.js
@@ -58,8 +58,10 @@ async function loadMarkdownFilePromise(post) {
 	let output = '---\n';
 	Object.entries(post.frontmatter).forEach(pair => {
 		const key = pair[0];
-		const value = (pair[1] || '').replace(/"/g, '\\"');
-		output += key + ': "' + value + '"\n';
+		const value = Array.isArray(pair[1])
+			? (pair[1].length === 0 ? "" : "\n  - \"" + pair[1].join("\"\n  - \"") + "\"")
+			: '"' + (pair[1] || '').replace(/"/g, '\\"') +'"';
+		output += key + ': ' + value + '\n';
 	});
 	output += '---\n\n' + post.content + '\n';
 	return output;