diff --git a/mitm.rb b/mitm.rb
index 288ce5f..efe69cb 100755
--- a/mitm.rb
+++ b/mitm.rb
@@ -16,18 +16,23 @@ while true
   activities[0].each do |activity|
     data = activity.readpartial(16+1+5)
     line = data.unpack("C*").collect { |b| sprintf("%02X ",b) }.join
-    begin
-      telegram = Telegram.parse(data)
-    rescue Exception => e
-      puts e.to_s
-    end
     if activity==pc_serial then
       puts "pc->ps: "+line
-      puts "pc->ps: "+telegram.to_s if telegram
+      begin
+        telegram = Telegram.parse(data)
+        puts "pc->ps: "+telegram.to_s if telegram
+      rescue Exception => e
+        puts e.to_s
+      end
       ps_serial.write(data)
     elsif activity==ps_serial then
       puts "ps->pc: "+line
-      puts "ps->pc: "+telegram.to_s if telegram
+      begin
+        telegram = Telegram.parse(data)
+        puts "ps->pc: "+telegram.to_s if telegram
+      rescue Exception => e
+        puts e.to_s
+      end
       pc_serial.write(data)
     else
       raise "unknown source"