diff --git a/public/s/css/f0ckm.css b/public/s/css/f0ckm.css
index bb926c5..5c0d4fa 100644
--- a/public/s/css/f0ckm.css
+++ b/public/s/css/f0ckm.css
@@ -1987,6 +1987,18 @@ body.sidebar-right-hidden .global-sidebar-right {
   border: 1px solid rgba(255, 255, 255, 0.1);
 }
 
+/* Shimmer placeholder while avatar image is still loading */
+.sidebar-avatar:not(.loaded) {
+  background: linear-gradient(90deg,
+      rgba(255, 255, 255, 0.04) 0%,
+      rgba(255, 255, 255, 0.10) 40%,
+      rgba(255, 255, 255, 0.04) 80%);
+  background-size: 600px 100%;
+  animation: skeleton-shimmer 1.6s ease-in-out infinite;
+  /* Keep border-box sizing consistent with the border already on .sidebar-avatar */
+  box-sizing: border-box;
+}
+
 .read-more-btn,
 .see-less-btn {
   display: inline;
diff --git a/public/s/js/sidebar-activity.js b/public/s/js/sidebar-activity.js
index 817e736..39d165c 100644
--- a/public/s/js/sidebar-activity.js
+++ b/public/s/js/sidebar-activity.js
@@ -473,7 +473,7 @@
                     <div class="comment-header">
                         <div class="comment-header-left">
                             <a href="/user/${c.username.toLowerCase()}" class="sidebar-avatar-link">
-                                <img src="${avatarSrc}" class="sidebar-avatar" alt="${c.username}" loading="eager" />
+                                <img src="${avatarSrc}" class="sidebar-avatar" alt="${c.username}" loading="eager" onload="this.classList.add('loaded')" onerror="this.classList.add('loaded');this.src='/a/default.png'" />
                             </a>
                             <a href="/user/${c.username.toLowerCase()}" class="comment-author" ${c.username_color ? `style="color: ${c.username_color}"` : ''}>${escapeHtml(c.display_name || c.username)}</a>
                         </div>