diff --git a/pyasic/miners/backends/bmminer.py b/pyasic/miners/backends/bmminer.py
index 511b256a..66b0ea26 100644
--- a/pyasic/miners/backends/bmminer.py
+++ b/pyasic/miners/backends/bmminer.py
@@ -238,9 +238,12 @@ class BMMiner(BaseMiner):
                     real_slots = []
 
                     for i in range(board_offset, board_offset + 4):
-                        key = f'chain_acs{i}'
-                        if boards[1][key] != '':
-                            real_slots.append(i)
+                        try:
+                            key = f'chain_acs{i}'
+                            if boards[1].get(key, '') != '':
+                                real_slots.append(i)
+                        except LookupError:
+                            pass
 
                     if len(real_slots) < 3:
                         real_slots = list(range(board_offset, board_offset + self.ideal_hashboards))