diff --git a/app/models/device.rb b/app/models/device.rb
index 752550b..36fd0d4 100644
--- a/app/models/device.rb
+++ b/app/models/device.rb
@@ -34,6 +34,9 @@ def prune
       # Delete messages not included in kept_messages
       mqtt_messages.each do |message|
         unless kept_messages.include?(message.id)
+          # Remove associated readings first
+          message.readings.destroy_all
+          # And then remove the message itself
           message.destroy
         end
       end