diff --git a/web.rb b/web.rb
index 5da7aa5943d78f5057ce3e52069b46a2916ac696..2681a3b5817f115426022e089f7cbf914933abec 100644
--- a/web.rb
+++ b/web.rb
@@ -200,6 +200,10 @@ class Web < Roda
 						end
 
 						r.post "transcription" do
+							duration = Time.parse(params["endTime"]) -
+							           Time.parse(params["startTime"])
+							next "OK<5" unless duration > 5
+
 							CustomerRepo.new.find_by_tel(params["to"]).then do |customer|
 								m = Blather::Stanza::Message.new
 								m.chat_state = nil