diff --git a/i80/pd.py b/i80/pd.py
index e06b9e4..9043444 100644
--- a/i80/pd.py
+++ b/i80/pd.py
@@ -136,6 +136,9 @@ class Decoder(srd.Decoder):
         have_hre = self.has_channel(21)
         hre_active_low = self.options['hre_polarity'] == 'low'
 
+        if not have_hwe and not have_hre:
+            raise ChannelError('Either hre or hwe must be set!')
+
         cs_active_low = self.options['cs_polarity'] == 'low'
         cmd_active_low = self.options['cmd_polarity'] == 'low'
         rst_active_low = self.options['rst_polarity'] == 'low'