diff --git a/lib/cooked_post_processor.rb b/lib/cooked_post_processor.rb
index 182e4ae7758..c58562d5c01 100644
--- a/lib/cooked_post_processor.rb
+++ b/lib/cooked_post_processor.rb
@@ -60,12 +60,7 @@ class CookedPostProcessor
 
   def post_process_images
     extract_images.each do |img|
-      src = img["src"].sub(/^https?:/i, "")
-      if large_images.include?(src)
-        add_large_image_placeholder!(img)
-      elsif broken_images.include?(src)
-        add_broken_image_placeholder!(img)
-      else
+      unless add_image_placeholder!(img)
         limit_size!(img)
         convert_to_link!(img)
       end
@@ -90,6 +85,18 @@ class CookedPostProcessor
     end
   end
 
+  def add_image_placeholder!(img)
+    src = img["src"].sub(/^https?:/i, "")
+
+    if large_images.include?(src)
+      return add_large_image_placeholder!(img)
+    elsif broken_images.include?(src)
+      return add_broken_image_placeholder!(img)
+    end
+
+    false
+  end
+
   def add_large_image_placeholder!(img)
     url = img["src"]
 
@@ -127,6 +134,7 @@ class CookedPostProcessor
     end
 
     img.remove
+    true
   end
 
   def add_broken_image_placeholder!(img)
@@ -136,6 +144,7 @@ class CookedPostProcessor
     img.remove_attribute("src")
     img.remove_attribute("width")
     img.remove_attribute("height")
+    true
   end
 
   def large_images
@@ -167,6 +176,8 @@ class CookedPostProcessor
     @doc.css("img[src^='data']") -
     # minus emojis
     @doc.css("img.emoji") -
+    # minus oneboxed images
+    oneboxed_images -
     # minus images inside quotes
     @doc.css(".quote img")
   end
@@ -442,8 +453,10 @@ class CookedPostProcessor
       img_classes = (img["class"] || "").split(" ")
       link_classes = ((parent&.name == "a" && parent["class"]) || "").split(" ")
 
-      if large_images.include?(src) || broken_images.include?(src)
-        img.remove unless img_classes.include?("onebox") || link_classes.include?("onebox")
+      if img_classes.include?("onebox") || link_classes.include?("onebox")
+        next if add_image_placeholder!(img)
+      elsif large_images.include?(src) || broken_images.include?(src)
+        img.remove
         next
       end
 
diff --git a/spec/components/cooked_post_processor_spec.rb b/spec/components/cooked_post_processor_spec.rb
index d7eae5b44d0..5cfb1c64b37 100644
--- a/spec/components/cooked_post_processor_spec.rb
+++ b/spec/components/cooked_post_processor_spec.rb
@@ -178,6 +178,22 @@ describe CookedPostProcessor do
         expect(cpp).to be_dirty
       end
 
+      describe 'when image is inside onebox' do
+        let(:url) { 'https://image.com/my-avatar' }
+        let(:post) { Fabricate(:post, raw: url) }
+
+        before do
+          Oneboxer.stubs(:onebox).with(url, anything).returns("<img class='onebox' src='/uploads/default/original/1X/1234567890123456.jpg' />")
+        end
+
+        it 'should not add lightbox' do
+          cpp.post_process_oneboxes
+          cpp.post_process_images
+
+          expect(cpp.html).to match_html("<p><img class=\"onebox\" src=\"/uploads/default/original/1X/1234567890123456.jpg\" width=\"690\"\ height=\"788\"></p>")
+        end
+      end
+
       describe 'when image is an svg' do
         let(:post) do
           Fabricate(:post, raw: '<img src="/uploads/default/original/1X/1234567890123456.svg">')