diff --git a/Marlin/src/lcd/anycubic_serial.cpp b/Marlin/src/lcd/anycubic_serial.cpp
index cb084925..a63f0ca5 100755
--- a/Marlin/src/lcd/anycubic_serial.cpp
+++ b/Marlin/src/lcd/anycubic_serial.cpp
@@ -66,7 +66,7 @@ ring_buffer tx_buffer_ajg = {{0}, 0, 0};
 
 inline void store_char(unsigned char c, ring_buffer *buffer)
 {
-  int i = (unsigned int)(buffer->head + 1) % SERIAL_BUFFER_SIZE;
+  unsigned int i = ((unsigned int)(buffer->head + 1)) % SERIAL_BUFFER_SIZE;
 
   // if we should be storing the received character into the location
   // just before the tail (meaning that the head would advance to the