diff --git a/app/assets/javascripts/discourse/app/lib/hashtag-types/category.js b/app/assets/javascripts/discourse/app/lib/hashtag-types/category.js
index ffb8f3001d4..e37a8e6617b 100644
--- a/app/assets/javascripts/discourse/app/lib/hashtag-types/category.js
+++ b/app/assets/javascripts/discourse/app/lib/hashtag-types/category.js
@@ -31,6 +31,10 @@ export default class CategoryHashtagType extends HashtagTypeBase {
   }
 
   generateIconHTML(hashtag) {
-    return `<span class="hashtag-category-badge hashtag-color--${this.type}-${hashtag.id}"></span>`;
+    const hashtagId = parseInt(hashtag.id, 10);
+    const colorCssClass = !this.preloadedData.mapBy("id").includes(hashtagId)
+      ? "hashtag-missing"
+      : `hashtag-color--${this.type}-${hashtag.id}`;
+    return `<span class="hashtag-category-badge ${colorCssClass}"></span>`;
   }
 }
diff --git a/app/assets/stylesheets/common/components/hashtag.scss b/app/assets/stylesheets/common/components/hashtag.scss
index ab328819ddb..9c9825d9d28 100644
--- a/app/assets/stylesheets/common/components/hashtag.scss
+++ b/app/assets/stylesheets/common/components/hashtag.scss
@@ -25,6 +25,10 @@ a.hashtag {
   .d-icon {
     font-size: var(--font-down-1);
     margin: 0 0.2em 0 0.1em;
+
+    &.hashtag-missing {
+      color: var(--primary-medium);
+    }
   }
 
   img.emoji {
@@ -43,6 +47,10 @@ a.hashtag {
     height: 9px;
     margin-right: 5px;
     display: inline-block;
+
+    &.hashtag-missing {
+      background-color: var(--primary-medium);
+    }
   }
 }
 
diff --git a/plugins/chat/assets/javascripts/discourse/lib/hashtag-types/channel.js b/plugins/chat/assets/javascripts/discourse/lib/hashtag-types/channel.js
index 5e49cb37e31..f49216bbb38 100644
--- a/plugins/chat/assets/javascripts/discourse/lib/hashtag-types/channel.js
+++ b/plugins/chat/assets/javascripts/discourse/lib/hashtag-types/channel.js
@@ -25,8 +25,12 @@ export default class ChannelHashtagType extends HashtagTypeBase {
   }
 
   generateIconHTML(hashtag) {
+    const hashtagId = parseInt(hashtag.id, 10);
+    const colorCssClass = !this.preloadedData.mapBy("id").includes(hashtagId)
+      ? "hashtag-missing"
+      : `hashtag-color--${this.type}-${hashtag.id}`;
     return iconHTML(hashtag.icon, {
-      class: `hashtag-color--${this.type}-${hashtag.id}`,
+      class: colorCssClass,
     });
   }
 }
diff --git a/plugins/chat/spec/system/hashtag_autocomplete_spec.rb b/plugins/chat/spec/system/hashtag_autocomplete_spec.rb
index 2973832dd67..d7d3c7d5ec4 100644
--- a/plugins/chat/spec/system/hashtag_autocomplete_spec.rb
+++ b/plugins/chat/spec/system/hashtag_autocomplete_spec.rb
@@ -80,4 +80,44 @@ describe "Using #hashtag autocompletion to search for and lookup channels",
     <a class=\"hashtag-cooked\" href=\"#{tag.url}\" data-type=\"tag\" data-slug=\"razed\" data-id="#{tag.id}"><svg class=\"fa d-icon d-icon-tag svg-icon hashtag-color--tag-#{tag.id} svg-string\" xmlns=\"http://www.w3.org/2000/svg\"><use href=\"#tag\"></use></svg><span>razed</span></a>
     HTML
   end
+
+  context "when a user cannot access the category for a cooked channel hashtag" do
+    fab!(:admin) { Fabricate(:admin) }
+    fab!(:manager_group) { Fabricate(:group, name: "Managers") }
+    fab!(:private_category) do
+      Fabricate(:private_category, name: "Management", slug: "management", group: manager_group)
+    end
+    fab!(:admin_group_user) { Fabricate(:group_user, user: admin, group: manager_group) }
+    fab!(:management_channel) do
+      Fabricate(:chat_channel, chatable: private_category, slug: "management")
+    end
+    fab!(:post_with_private_category) do
+      Fabricate(
+        :post,
+        topic: topic,
+        raw: "this is a secret #management::channel channel",
+        user: admin,
+      )
+    end
+    fab!(:message_with_private_channel) do
+      Fabricate(
+        :chat_message,
+        chat_channel: channel1,
+        user: admin,
+        message: "this is a secret #management channel",
+      )
+    end
+
+    before { management_channel.add(admin) }
+
+    it "shows a default color and css class for the channel icon in a post" do
+      topic_page.visit_topic(topic, post_number: post_with_private_category.post_number)
+      expect(page).to have_css(".hashtag-cooked .hashtag-missing")
+    end
+
+    it "shows a default color and css class for the channel icon in a channel" do
+      chat_page.visit_channel(channel1)
+      expect(page).to have_css(".hashtag-cooked .hashtag-missing")
+    end
+  end
 end
diff --git a/spec/system/hashtag_autocomplete_spec.rb b/spec/system/hashtag_autocomplete_spec.rb
index cc7d40a94df..da22f0728fd 100644
--- a/spec/system/hashtag_autocomplete_spec.rb
+++ b/spec/system/hashtag_autocomplete_spec.rb
@@ -93,4 +93,21 @@ describe "Using #hashtag autocompletion to search for and lookup categories and
     <a class=\"hashtag-cooked\" href=\"#{tag.url}\" data-type=\"tag\" data-slug=\"cooltag\" data-id=\"#{tag.id}\"><svg class=\"fa d-icon d-icon-tag svg-icon hashtag-color--tag-#{tag.id} svg-string\" xmlns=\"http://www.w3.org/2000/svg\"><use href=\"#tag\"></use></svg><span>cooltag</span></a>
     HTML
   end
+
+  context "when a user cannot access the category for a hashtag cooked in another post" do
+    fab!(:admin) { Fabricate(:admin) }
+    fab!(:manager_group) { Fabricate(:group, name: "Managers") }
+    fab!(:private_category) do
+      Fabricate(:private_category, name: "Management", slug: "management", group: manager_group)
+    end
+    fab!(:admin_group_user) { Fabricate(:group_user, user: admin, group: manager_group) }
+    fab!(:post_with_private_category) do
+      Fabricate(:post, topic: topic, raw: "this is a secret #management category", user: admin)
+    end
+
+    it "shows a default color and css class for the category icon square" do
+      topic_page.visit_topic(topic, post_number: post_with_private_category.post_number)
+      expect(page).to have_css(".hashtag-cooked .hashtag-missing")
+    end
+  end
 end
diff --git a/spec/system/page_objects/pages/topic.rb b/spec/system/page_objects/pages/topic.rb
index dbc56fe3d40..15b7e23c926 100644
--- a/spec/system/page_objects/pages/topic.rb
+++ b/spec/system/page_objects/pages/topic.rb
@@ -8,8 +8,10 @@ module PageObjects
         @fast_edit_component = PageObjects::Components::FastEditor.new
       end
 
-      def visit_topic(topic)
-        page.visit "/t/#{topic.id}"
+      def visit_topic(topic, post_number: nil)
+        url = "/t/#{topic.id}"
+        url += "/#{post_number}" if post_number
+        page.visit url
         self
       end