diff --git a/Marlin/src/pins/pins_postprocess.h b/Marlin/src/pins/pins_postprocess.h
index 50757c9bf2fa..ac81eb3f25ba 100644
--- a/Marlin/src/pins/pins_postprocess.h
+++ b/Marlin/src/pins/pins_postprocess.h
@@ -1417,7 +1417,7 @@
     #define U_STEP_PIN   _EPIN(U_E_INDEX, STEP)
     #define U_DIR_PIN    _EPIN(U_E_INDEX, DIR)
     #define U_ENABLE_PIN _EPIN(U_E_INDEX, ENABLE)
-    #if M_E_INDEX >= MAX_E_STEPPERS || !PIN_EXISTS(U_STEP)
+    #if U_E_INDEX >= MAX_E_STEPPERS || !PIN_EXISTS(U_STEP)
       #error "No E stepper plug left for U!"
     #else
       #define AUTO_ASSIGNED_U_STEPPER 1