diff --git a/kmk/modules/split.py b/kmk/modules/split.py
index 164a9a25e..bbf9cfc67 100644
--- a/kmk/modules/split.py
+++ b/kmk/modules/split.py
@@ -140,7 +140,7 @@ def during_bootup(self, keyboard):
                     )
 
         # Attempt to sanely guess a coord_mapping if one is not provided.
-        if not keyboard.coord_mapping:
+        if not keyboard.coord_mapping and keyboard.row_pins and keyboard.col_pins:
             cm = []
 
             rows_to_calc = len(keyboard.row_pins)
@@ -158,6 +158,8 @@ def during_bootup(self, keyboard):
                     cm.append(cols_to_calc * (rows_to_calc + ridx) + cidx)
 
             keyboard.coord_mapping = tuple(cm)
+        else:
+            print('Error: please provide coord_mapping for custom scanner')
 
         if self.split_side == SplitSide.RIGHT:
             offset = self.split_offset