Tweak BLOCK_BUFFER_SIZE description

Marlin/src/inc/SanityCheck.h

@@ -1473,6 +1473,10 @@ static_assert(COUNT(sanity_arr_3) <= XYZE_N, "DEFAULT_MAX_ACCELERATION has too m
   #error "CNC_COORDINATE_SYSTEMS is incompatible with NO_WORKSPACE_OFFSETS."
 #endif
 
+#if !BLOCK_BUFFER_SIZE || !IS_POWER_OF_2(BLOCK_BUFFER_SIZE)
+  #error "BLOCK_BUFFER_SIZE must be a power of 2."
+#endif
+
 #include "../HAL/HAL_SanityCheck.h"  // get CPU specific checks
 
 #endif // _SANITYCHECK_H_