diff --git a/db/migrate/20171228122834_replace_blocked_silence_translation.rb b/db/migrate/20171228122834_replace_blocked_silence_translation.rb
index 06ce33ed13f..dfd9a02c0ff 100644
--- a/db/migrate/20171228122834_replace_blocked_silence_translation.rb
+++ b/db/migrate/20171228122834_replace_blocked_silence_translation.rb
@@ -1,8 +1,17 @@
 class ReplaceBlockedSilenceTranslation < ActiveRecord::Migration[5.1]
   def change
     execute <<~SQL
-      UPDATE translation_overrides SET translation_key = 'system_messages.silenced_by_staff.subject_template' WHERE translation_key = 'system_messages.blocked_by_staff.subject_template';
-      UPDATE translation_overrides SET translation_key = 'system_messages.silenced_by_staff.text_body_template' WHERE translation_key = 'system_messages.blocked_by_staff.text_body_template';
+      UPDATE translation_overrides
+      SET translation_key = 'system_messages.silenced_by_staff.subject_template'
+      WHERE translation_key = 'system_messages.blocked_by_staff.subject_template'
+      AND NOT EXISTS (SELECT 1 FROM translation_overrides WHERE translation_key = 'system_messages.silenced_by_staff.subject_template');
+    SQL
+
+    execute <<~SQL
+      UPDATE translation_overrides
+      SET translation_key = 'system_messages.silenced_by_staff.text_body_template'
+      WHERE translation_key = 'system_messages.blocked_by_staff.text_body_template'
+      AND NOT EXISTS (SELECT 1 FROM translation_overrides WHERE translation_key = 'system_messages.silenced_by_staff.text_body_template');
     SQL
   end
 end