diff --git a/lib/tasks/seek_upgrades.rake b/lib/tasks/seek_upgrades.rake
index 769e95aed1..8bf3e7f183 100644
--- a/lib/tasks/seek_upgrades.rake
+++ b/lib/tasks/seek_upgrades.rake
@@ -18,6 +18,7 @@ namespace :seek do
     implement_assay_streams_for_isa_assays
     set_ls_login_legacy_mode
     rename_custom_metadata_legacy_supported_type
+    fix_xlsx_marked_as_zip
   ]
 
   # these are the tasks that are executes for each upgrade as standard, and rarely change
@@ -205,6 +206,15 @@ namespace :seek do
     end
   end
 
+  task(fix_xlsx_marked_as_zip: [:environment]) do
+    blobs = ContentBlob.where('original_filename LIKE ?','%.xlsx').where(content_type: 'application/zip')
+    if blobs.any?
+      n = blobs.count
+      blobs.update_all(content_type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet')
+      puts "... fixed #{n} XLSX blobs with zip content type"
+    end
+  end
+
   private
 
   ##