diff --git a/lib/onewire/onewire.py b/lib/onewire/onewire.py
index 0b3b35a..6b32cd8 100644
--- a/lib/onewire/onewire.py
+++ b/lib/onewire/onewire.py
@@ -182,7 +182,6 @@ def start_convertion(self, rom=None):
         if (rom==None) and (len(self.roms)>0):
             rom=self.roms[0]
         if rom!=None:    
-            rom = rom or self.roms[0]
             ow = self.ow
             ow.reset()
             ow.select_rom(rom)