diff --git a/app/services/concerns/iiif_thumbnail_paths.rb b/app/services/concerns/iiif_thumbnail_paths.rb
index e33ccc353..405ff24e9 100644
--- a/app/services/concerns/iiif_thumbnail_paths.rb
+++ b/app/services/concerns/iiif_thumbnail_paths.rb
@@ -22,8 +22,13 @@ def iiif_thumbnail_path(file_set, size)
       )
     end
 
-    def thumbnail?(_thumbnail)
-      true
+    # @param [FileSet] thumbnail the object that is the thumbnail
+    # @return [boolean] true when a thumbnail (either generated or a common asset)
+    #                   is expected to be available on the file system
+    def thumbnail?(thumbnail)
+      return true if thumbnail.image? || thumbnail.pdf? || thumbnail.office_document? ||
+                     thumbnail.audio? || thumbnail.video?
+      super(thumbnail)
     end
   end
 end
diff --git a/spec/services/iiif_work_thumbnail_path_service_spec.rb b/spec/services/iiif_work_thumbnail_path_service_spec.rb
index 3c2df0c6b..c3806c81b 100644
--- a/spec/services/iiif_work_thumbnail_path_service_spec.rb
+++ b/spec/services/iiif_work_thumbnail_path_service_spec.rb
@@ -39,5 +39,14 @@
 
       it { is_expected.to eq '/downloads/s1784k724?file=thumbnail' }
     end
+
+    context "with an unsupported mime type" do
+      let(:file) do
+        double(id: 's1/78/4k/72/s1784k724/files/6185235a-79b2-4c29-8c24-4d6ad9b11470',
+               mime_type: 'text/example')
+      end
+
+      it { is_expected.to match %r{^\/assets\/work-\w+\.png$} }
+    end
   end
 end