diff --git a/app/components/post_gallery_component.rb b/app/components/post_gallery_component.rb
index 95349b9ae..fa330a4f6 100644
--- a/app/components/post_gallery_component.rb
+++ b/app/components/post_gallery_component.rb
@@ -7,6 +7,10 @@
 #   seen in parent/child post sets.
 #
 class PostGalleryComponent < ApplicationComponent
+  # The default size of thumbnails in a gallery. See also PostPreviewComponent::DEFAULT_SIZE
+  # for the default size of standalone thumbnails.
+  DEFAULT_SIZE = "180"
+
   attr_reader :inline, :size, :options
 
   # The list of posts in the gallery.
@@ -20,7 +24,7 @@ class PostGalleryComponent < ApplicationComponent
   # @param size [String] The size of thumbnails in the gallery. Can be "150",
   #   "180", "225", "225w", "270", "270w", or "360".
   # @param options [Hash] A set of options given to the PostPreviewComponent.
-  def initialize(inline: false, size: PostPreviewComponent::DEFAULT_SIZE, **options)
+  def initialize(inline: false, size: DEFAULT_SIZE, **options)
     super
     @inline = inline
     @options = options
@@ -28,7 +32,7 @@ class PostGalleryComponent < ApplicationComponent
     if size.to_s.in?(PostPreviewComponent::SIZES)
       @size = size
     else
-      @size = PostPreviewComponent::DEFAULT_SIZE
+      @size = DEFAULT_SIZE
     end
   end
 
diff --git a/app/components/post_gallery_component/post_gallery_component.scss b/app/components/post_gallery_component/post_gallery_component.scss
index ed2bbd9ce..13631cdf4 100644
--- a/app/components/post_gallery_component/post_gallery_component.scss
+++ b/app/components/post_gallery_component/post_gallery_component.scss
@@ -43,7 +43,7 @@
       gap: 0.25rem;
     }
 
-    &.post-gallery-150  .posts-container { grid-template-columns: repeat(2, auto); }
+    &.post-gallery-150  .posts-container { grid-template-columns: repeat(3, minmax(0, 150px)); }
     &.post-gallery-180  .posts-container { grid-template-columns: repeat(2, auto); }
     &.post-gallery-225  .posts-container { grid-template-columns: repeat(2, auto); }
     &.post-gallery-225w .posts-container { grid-template-columns: repeat(2, auto); }
diff --git a/app/components/post_preview_component.rb b/app/components/post_preview_component.rb
index de5eb5eea..7c55fdc63 100644
--- a/app/components/post_preview_component.rb
+++ b/app/components/post_preview_component.rb
@@ -1,7 +1,9 @@
 # frozen_string_literal: true
 
 class PostPreviewComponent < ApplicationComponent
-  DEFAULT_SIZE = "150"
+  # The default size of standalone thumbnails not in a gallery. See also
+  # PostGalleryComponent::DEFAULT_SIZE for the default size of thumbnails in a gallery.
+  DEFAULT_SIZE = "180"
 
   SIZES = %w[150 180 225 225w 270 270w 360]
 
diff --git a/app/controllers/posts_controller.rb b/app/controllers/posts_controller.rb
index 306943979..f9a25f414 100644
--- a/app/controllers/posts_controller.rb
+++ b/app/controllers/posts_controller.rb
@@ -18,7 +18,7 @@ class PostsController < ApplicationController
       tag_query = params[:tags] || params.dig(:post, :tags)
       @show_votes = (params[:show_votes].presence || cookies[:post_preview_show_votes].presence || "false").truthy?
       @post_set = PostSets::Post.new(tag_query, params[:page], params[:limit], format: request.format.symbol, show_votes: @show_votes)
-      @preview_size = params[:size].presence || cookies[:post_preview_size].presence || PostPreviewComponent::DEFAULT_SIZE
+      @preview_size = params[:size].presence || cookies[:post_preview_size].presence || PostGalleryComponent::DEFAULT_SIZE
       @posts = authorize @post_set.posts, policy_class: PostPolicy
       @post_set.log!
       respond_with(@posts) do |format|
@@ -60,7 +60,7 @@ class PostsController < ApplicationController
     @post = authorize Post.find(params[:id])
     @post.update(permitted_attributes(@post))
     @show_votes = (params[:show_votes].presence || cookies[:post_preview_show_votes].presence || "false").truthy?
-    @preview_size = params[:size].presence || cookies[:post_preview_size].presence || PostPreviewComponent::DEFAULT_SIZE
+    @preview_size = params[:size].presence || cookies[:post_preview_size].presence || PostGalleryComponent::DEFAULT_SIZE
     respond_with_post_after_update(@post)
   end
 
diff --git a/app/views/posts/partials/show/_child_notice.html.erb b/app/views/posts/partials/show/_child_notice.html.erb
index 963d079c0..aa90bd128 100644
--- a/app/views/posts/partials/show/_child_notice.html.erb
+++ b/app/views/posts/partials/show/_child_notice.html.erb
@@ -4,5 +4,5 @@ This post has <%= link_to pluralize(children.length, "child"), posts_path(tags:
 <%= link_to("« hide", "#", id: "has-children-relationship-preview-link") %>
 
 <div id="has-children-relationship-preview">
-  <%= render_post_gallery([parent, *children], tags: "parent:#{parent.id}", show_deleted: true, inline: true) %>
+  <%= render_post_gallery([parent, *children], tags: "parent:#{parent.id}", show_deleted: true, inline: true, size: "150") %>
 </div>
diff --git a/app/views/posts/partials/show/_parent_notice.html.erb b/app/views/posts/partials/show/_parent_notice.html.erb
index 339825a7c..e6b4500ef 100644
--- a/app/views/posts/partials/show/_parent_notice.html.erb
+++ b/app/views/posts/partials/show/_parent_notice.html.erb
@@ -10,5 +10,5 @@ This post belongs to a <%= link_to "parent", posts_path(tags: "parent:#{parent.i
 <%= link_to "« hide", "#", id: "has-parent-relationship-preview-link" %>
 
 <div id="has-parent-relationship-preview">
-  <%= render_post_gallery([parent, *children], tags: "parent:#{parent.id}", show_deleted: true, inline: true) %>
+  <%= render_post_gallery([parent, *children], tags: "parent:#{parent.id}", show_deleted: true, inline: true, size: "150") %>
 </div>
diff --git a/test/components/post_preview_component_test.rb b/test/components/post_preview_component_test.rb
index f42591b28..3aab74012 100644
--- a/test/components/post_preview_component_test.rb
+++ b/test/components/post_preview_component_test.rb
@@ -14,7 +14,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: User.anonymous)
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
       end
     end
 
@@ -24,7 +24,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: User.anonymous)
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
         assert_equal("0:01", node.css("article .post-duration").text.strip)
       end
     end
@@ -35,7 +35,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: User.anonymous)
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
         assert(node.css("article .sound-icon").present?)
       end
     end
@@ -50,7 +50,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: create(:gold_user))
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
       end
 
       should "not be visible to Members" do
@@ -68,7 +68,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: create(:gold_user))
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
       end
 
       should "not be visible to Members" do
@@ -86,7 +86,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: create(:approver))
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
       end
 
       should "not be visible to Gold users" do
@@ -104,7 +104,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: User.anonymous)
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
       end
 
       should "not be visible to users with safe mode on" do
@@ -124,7 +124,7 @@ class PostPreviewComponentTest < ViewComponent::TestCase
         node = render_preview(@post, current_user: User.anonymous, show_deleted: true)
 
         assert_equal(post_path(@post), node.css("article a").attr("href").value)
-        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+        assert_equal(@post.media_asset.variant("180x180").file_url, node.css("article img").attr("src").value)
       end
 
       should "not be visible to users normally" do