diff --git a/Marlin/src/feature/Max7219_Debug_LEDs.h b/Marlin/src/feature/Max7219_Debug_LEDs.h
index 3523eef40..8b3d19e18 100644
--- a/Marlin/src/feature/Max7219_Debug_LEDs.h
+++ b/Marlin/src/feature/Max7219_Debug_LEDs.h
@@ -47,6 +47,9 @@
 #endif
 #define _ROT ((MAX7219_ROTATE + 360) % 360)
 
+#ifndef MAX7219_NUMBER_UNITS
+  #define MAX7219_NUMBER_UNITS 1
+#endif
 #define MAX7219_LINES (8 * (MAX7219_NUMBER_UNITS))
 
 #if _ROT == 0 || _ROT == 180