diff --git a/lib/plugins/tag/post_link.ts b/lib/plugins/tag/post_link.ts
index 67289df469..9aec591a9d 100644
--- a/lib/plugins/tag/post_link.ts
+++ b/lib/plugins/tag/post_link.ts
@@ -41,7 +41,13 @@ export = (ctx: Hexo) => {
     const attrTitle = escapeHTML(post.title || post.slug);
     if (escape === 'true') title = escapeHTML(title);
 
-    const url = new URL(post.path, ctx.config.url).pathname + (hash ? `#${hash}` : '');
+    // guarantee the base url ends with a slash. (case of using a subdirectory in the url of the site)
+    let baseUrl = ctx.config.url;
+    if (!baseUrl.endsWith('/')) {
+      baseUrl += '/';
+    }
+
+    const url = new URL(post.path, baseUrl).pathname + (hash ? `#${hash}` : '');
     const link = encodeURL(url);
 
     return `<a href="${link}" title="${attrTitle}">${title}</a>`;
diff --git a/test/scripts/tags/post_link.js b/test/scripts/tags/post_link.js
index 05839a8098..8d4d89f546 100644
--- a/test/scripts/tags/post_link.js
+++ b/test/scripts/tags/post_link.js
@@ -77,4 +77,9 @@ describe('post_link', () => {
   it('should keep hash', () => {
     postLink(['foo#bar']).should.eql('<a href="/foo/#bar" title="Hello world">Hello world</a>');
   });
+
+  it('should keep subdir', () => {
+    hexo.config.url = 'http://example.com/subdir';
+    postLink(['foo']).should.eql('<a href="/subdir/foo/" title="Hello world">Hello world</a>');
+  });
 });