diff --git a/boards/static/css/md/base_page.css b/boards/static/css/md/base_page.css
--- a/boards/static/css/md/base_page.css
+++ b/boards/static/css/md/base_page.css
@@ -477,6 +477,7 @@ ul {
 .post_preview {
     border-left: 1px solid #777;
     border-right: 1px solid #777;
+    max-width: 600px;
 }
 
 /* Code highlighter */