Disable currency update of discontinued currency?

I have some closed accounts in German Marks (DEM). My base currency is USD.
Every time I do an online price update it tells me that it can’t get a value for USD-DEM and DEM-USD. Is there any way to tell Kmymoney to stop looking for a price for a specific currency or any currency that is only used in closed accounts?
Obviously I have lived with this for a while. DEM hasn’t been there and I just have to press continue when it can’t find the price to continue with the rest. Which is what I have been doing since we could not use yahoo for currency prices anymore.