diff --git a/lib/pretty_text.rb b/lib/pretty_text.rb
index 2f6417f89..d5786c147 100644
--- a/lib/pretty_text.rb
+++ b/lib/pretty_text.rb
@@ -224,6 +224,7 @@ module PrettyText
 
   def self.add_s3_cdn(doc)
     doc.css("img").each do |img|
+      next unless img["src"]
       img["src"] = img["src"].sub(Discourse.store.absolute_base_url, SiteSetting.s3_cdn_url)
     end
   end
diff --git a/spec/components/pretty_text_spec.rb b/spec/components/pretty_text_spec.rb
index 66a64a404..5da48e1e9 100644
--- a/spec/components/pretty_text_spec.rb
+++ b/spec/components/pretty_text_spec.rb
@@ -323,8 +323,9 @@ describe PrettyText do
     SiteSetting.s3_upload_bucket = "test"
     SiteSetting.s3_cdn_url = "https://awesome.cdn"
 
-    raw = "<img src='#{Discourse.store.absolute_base_url}/original/9/9/99c9384b8b6d87f8509f8395571bc7512ca3cad1.jpg'"
-    cooked = "<p><img src='https://awesome.cdn/original/9/9/99c9384b8b6d87f8509f8395571bc7512ca3cad1.jpg'></p>"
+    # add extra img tag to ensure it does not blow up
+    raw = "<img><img src='#{Discourse.store.absolute_base_url}/original/9/9/99c9384b8b6d87f8509f8395571bc7512ca3cad1.jpg'"
+    cooked = "<p><img><img src='https://awesome.cdn/original/9/9/99c9384b8b6d87f8509f8395571bc7512ca3cad1.jpg'></p>"
 
     expect(PrettyText.cook(raw)).to match_html(cooked)
   end