diff --git a/lib/forest_liana/schema_file_updater.rb b/lib/forest_liana/schema_file_updater.rb
index 9ffd606e..b37b537a 100644
--- a/lib/forest_liana/schema_file_updater.rb
+++ b/lib/forest_liana/schema_file_updater.rb
@@ -118,7 +118,7 @@ def initialize filename, collections, meta
 
       # NOTICE: Sort keys
       @collections = @collections.map do |collection|
-        collection['fields'].sort do |field1, field2|
+        collection['fields'].sort! do |field1, field2|
           [field1['field'], field1['type'].inspect] <=> [field2['field'], field2['type'].inspect]
         end