diff --git a/Marlin/src/core/serial.cpp b/Marlin/src/core/serial.cpp
index 7e53f38517..5871c61f99 100644
--- a/Marlin/src/core/serial.cpp
+++ b/Marlin/src/core/serial.cpp
@@ -34,7 +34,7 @@ PGMSTR(SP_X_STR, " X");  PGMSTR(SP_Y_STR, " Y");  PGMSTR(SP_Z_STR, " Z");  PGMST
 PGMSTR(SP_X_LBL, " X:"); PGMSTR(SP_Y_LBL, " Y:"); PGMSTR(SP_Z_LBL, " Z:"); PGMSTR(SP_E_LBL, " E:");
 
 #if HAS_MULTI_SERIAL
-  int8_t serial_port_index = 0;
+  serial_index_t serial_port_index = 0;
 #endif
 
 void serialprintPGM(PGM_P str) {
diff --git a/Marlin/src/core/serial.h b/Marlin/src/core/serial.h
index 1dd3cd9cd0..ae1ef4169f 100644
--- a/Marlin/src/core/serial.h
+++ b/Marlin/src/core/serial.h
@@ -61,9 +61,11 @@ extern uint8_t marlin_debug_flags;
 //
 // Serial redirection
 //
+typedef int8_t serial_index_t;
 #define SERIAL_BOTH 0x7F
+
 #if HAS_MULTI_SERIAL
-  extern int8_t serial_port_index;
+  extern serial_index_t serial_port_index;
   #define _PORT_REDIRECT(n,p)   REMEMBER(n,serial_port_index,p)
   #define _PORT_RESTORE(n)      RESTORE(n)
 
diff --git a/Marlin/src/feature/meatpack.cpp b/Marlin/src/feature/meatpack.cpp
index 631fa042db..cd6d8ce6b9 100644
--- a/Marlin/src/feature/meatpack.cpp
+++ b/Marlin/src/feature/meatpack.cpp
@@ -74,7 +74,6 @@ void MeatPack::reset_state() {
   second_char = 0;
   cmd_count = full_char_count = char_out_count = 0;
   TERN_(MP_DEBUG, chars_decoded = 0);
-  report_state();
 }
 
 /**
@@ -189,7 +188,7 @@ void MeatPack::report_state() {
  * Interpret a single character received from serial
  * according to the current meatpack state.
  */
-void MeatPack::handle_rx_char(const uint8_t c) {
+void MeatPack::handle_rx_char(const uint8_t c, const serial_index_t serial_ind) {
   if (c == kCommandByte) {                // A command (0xFF) byte?
     if (cmd_count) {                      // In fact, two in a row?
       cmd_is_next = true;                 // Then a MeatPack command follows
@@ -201,6 +200,7 @@ void MeatPack::handle_rx_char(const uint8_t c) {
   }
 
   if (cmd_is_next) {                      // Were two command bytes received?
+    PORT_REDIRECT(serial_ind);
     handle_command((MeatPack_Command)c);  // Then the byte is a MeatPack command
     cmd_is_next = false;
     return;
diff --git a/Marlin/src/feature/meatpack.h b/Marlin/src/feature/meatpack.h
index b895bcae50..2641130bd8 100644
--- a/Marlin/src/feature/meatpack.h
+++ b/Marlin/src/feature/meatpack.h
@@ -101,7 +101,7 @@ private:
 
   // Pass in a character rx'd by SD card or serial. Automatically parses command/ctrl sequences,
   // and will control state internally.
-  static void handle_rx_char(const uint8_t c);
+  static void handle_rx_char(const uint8_t c, const serial_index_t serial_ind);
 
   /**
    * After passing in rx'd char using above method, call this to get characters out.
diff --git a/Marlin/src/feature/spindle_laser.h b/Marlin/src/feature/spindle_laser.h
index 57fc136c8c..d50bc7eb42 100644
--- a/Marlin/src/feature/spindle_laser.h
+++ b/Marlin/src/feature/spindle_laser.h
@@ -157,7 +157,7 @@ public:
         #elif CUTTER_UNIT_IS(RPM)
           2
         #else
-          #error "CUTTER_UNIT_IS(???)"
+          #error "CUTTER_UNIT_IS(unknown)"
         #endif
       ));
     }
diff --git a/Marlin/src/gcode/host/M118.cpp b/Marlin/src/gcode/host/M118.cpp
index 27207b7172..7a77861e2b 100644
--- a/Marlin/src/gcode/host/M118.cpp
+++ b/Marlin/src/gcode/host/M118.cpp
@@ -53,7 +53,7 @@ void GcodeSuite::M118() {
   }
 
   #if HAS_MULTI_SERIAL
-    const int8_t old_serial = serial_port_index;
+    const serial_index_t old_serial = serial_port_index;
     if (WITHIN(port, 0, NUM_SERIAL))
       serial_port_index = (
         port == 0 ? SERIAL_BOTH
diff --git a/Marlin/src/gcode/queue.cpp b/Marlin/src/gcode/queue.cpp
index 51fec7d41c..1059997edb 100644
--- a/Marlin/src/gcode/queue.cpp
+++ b/Marlin/src/gcode/queue.cpp
@@ -89,7 +89,7 @@ char GCodeQueue::command_buffer[BUFSIZE][MAX_CMD_SIZE];
  * The port that the command was received on
  */
 #if HAS_MULTI_SERIAL
-  int16_t GCodeQueue::port[BUFSIZE];
+  serial_index_t GCodeQueue::port[BUFSIZE];
 #endif
 
 /**
@@ -136,11 +136,11 @@ void GCodeQueue::clear() {
  */
 void GCodeQueue::_commit_command(bool say_ok
   #if HAS_MULTI_SERIAL
-    , int16_t p/*=-1*/
+    , serial_index_t serial_ind/*=-1*/
   #endif
 ) {
   send_ok[index_w] = say_ok;
-  TERN_(HAS_MULTI_SERIAL, port[index_w] = p);
+  TERN_(HAS_MULTI_SERIAL, port[index_w] = serial_ind);
   TERN_(POWER_LOSS_RECOVERY, recovery.commit_sdpos(index_w));
   if (++index_w >= BUFSIZE) index_w = 0;
   length++;
@@ -153,14 +153,14 @@ void GCodeQueue::_commit_command(bool say_ok
  */
 bool GCodeQueue::_enqueue(const char* cmd, bool say_ok/*=false*/
   #if HAS_MULTI_SERIAL
-    , int16_t pn/*=-1*/
+    , serial_index_t serial_ind/*=-1*/
   #endif
 ) {
   if (*cmd == ';' || length >= BUFSIZE) return false;
   strcpy(command_buffer[index_w], cmd);
   _commit_command(say_ok
     #if HAS_MULTI_SERIAL
-      , pn
+      , serial_ind
     #endif
   );
   return true;
@@ -289,9 +289,9 @@ void GCodeQueue::enqueue_now_P(PGM_P const pgcode) {
  */
 void GCodeQueue::ok_to_send() {
   #if HAS_MULTI_SERIAL
-    const int16_t pn = command_port();
-    if (pn < 0) return;
-    PORT_REDIRECT(pn);                    // Reply to the serial port that sent the command
+    const serial_index_t serial_ind = command_port();
+    if (serial_ind < 0) return;                   // Never mind. Command came from SD or Flash Drive
+    PORT_REDIRECT(serial_ind);                    // Reply to the serial port that sent the command
   #endif
   if (!send_ok[index_r]) return;
   SERIAL_ECHOPGM(STR_OK);
@@ -314,14 +314,14 @@ void GCodeQueue::ok_to_send() {
  * indicate that a command needs to be re-sent.
  */
 void GCodeQueue::flush_and_request_resend() {
-  const int16_t pn = command_port();
+  const serial_index_t serial_ind = command_port();
   #if HAS_MULTI_SERIAL
-    if (pn < 0) return;
-    PORT_REDIRECT(pn);                    // Reply to the serial port that sent the command
+    if (serial_ind < 0) return;                   // Never mind. Command came from SD or Flash Drive
+    PORT_REDIRECT(serial_ind);                    // Reply to the serial port that sent the command
   #endif
   SERIAL_FLUSH();
   SERIAL_ECHOPGM(STR_RESEND);
-  SERIAL_ECHOLN(last_N[pn] + 1);
+  SERIAL_ECHOLN(last_N[serial_ind] + 1);
   ok_to_send();
 }
 
@@ -348,14 +348,14 @@ inline int read_serial(const uint8_t index) {
   }
 }
 
-void GCodeQueue::gcode_line_error(PGM_P const err, const int8_t pn) {
-  PORT_REDIRECT(pn);                      // Reply to the serial port that sent the command
+void GCodeQueue::gcode_line_error(PGM_P const err, const serial_index_t serial_ind) {
+  PORT_REDIRECT(serial_ind);                      // Reply to the serial port that sent the command
   SERIAL_ERROR_START();
   serialprintPGM(err);
-  SERIAL_ECHOLN(last_N[pn]);
-  while (read_serial(pn) != -1);          // Clear out the RX buffer
+  SERIAL_ECHOLN(last_N[serial_ind]);
+  while (read_serial(serial_ind) != -1);          // Clear out the RX buffer
   flush_and_request_resend();
-  serial_count[pn] = 0;
+  serial_count[serial_ind] = 0;
 }
 
 FORCE_INLINE bool is_M29(const char * const cmd) {  // matches "M29" & "M29 ", but not "M290", etc
@@ -473,13 +473,13 @@ void GCodeQueue::get_serial_commands() {
    * Loop while serial characters are incoming and the queue is not full
    */
   while (length < BUFSIZE && serial_data_available()) {
-    LOOP_L_N(i, NUM_SERIAL) {
+    LOOP_L_N(p, NUM_SERIAL) {
 
-      const int c = read_serial(i);
+      const int c = read_serial(p);
       if (c < 0) continue;
 
       #if ENABLED(MEATPACK)
-        meatpack.handle_rx_char(uint8_t(c));
+        meatpack.handle_rx_char(uint8_t(c), p);
         char c_res[2] = { 0, 0 };
         const uint8_t char_count = meatpack.get_result_char(c_res);
       #else
@@ -492,10 +492,10 @@ void GCodeQueue::get_serial_commands() {
         if (ISEOL(serial_char)) {
 
           // Reset our state, continue if the line was empty
-          if (process_line_done(serial_input_state[i], serial_line_buffer[i], serial_count[i]))
+          if (process_line_done(serial_input_state[p], serial_line_buffer[p], serial_count[p]))
             continue;
 
-          char* command = serial_line_buffer[i];
+          char* command = serial_line_buffer[p];
 
           while (*command == ' ') command++;                   // Skip leading spaces
           char *npos = (*command == 'N') ? command : nullptr;  // Require the N parameter to start the line
@@ -511,25 +511,25 @@ void GCodeQueue::get_serial_commands() {
 
             const long gcode_N = strtol(npos + 1, nullptr, 10);
 
-            if (gcode_N != last_N[i] + 1 && !M110)
-              return gcode_line_error(PSTR(STR_ERR_LINE_NO), i);
+            if (gcode_N != last_N[p] + 1 && !M110)
+              return gcode_line_error(PSTR(STR_ERR_LINE_NO), p);
 
             char *apos = strrchr(command, '*');
             if (apos) {
               uint8_t checksum = 0, count = uint8_t(apos - command);
               while (count) checksum ^= command[--count];
               if (strtol(apos + 1, nullptr, 10) != checksum)
-                return gcode_line_error(PSTR(STR_ERR_CHECKSUM_MISMATCH), i);
+                return gcode_line_error(PSTR(STR_ERR_CHECKSUM_MISMATCH), p);
             }
             else
-              return gcode_line_error(PSTR(STR_ERR_NO_CHECKSUM), i);
+              return gcode_line_error(PSTR(STR_ERR_NO_CHECKSUM), p);
 
-            last_N[i] = gcode_N;
+            last_N[p] = gcode_N;
           }
           #if ENABLED(SDSUPPORT)
             // Pronterface "M29" and "M29 " has no line number
             else if (card.flag.saving && !is_M29(command))
-              return gcode_line_error(PSTR(STR_ERR_NO_CHECKSUM), i);
+              return gcode_line_error(PSTR(STR_ERR_NO_CHECKSUM), p);
           #endif
 
           //
@@ -547,7 +547,7 @@ void GCodeQueue::get_serial_commands() {
                 #if ENABLED(BEZIER_CURVE_SUPPORT)
                   case 5:
                 #endif
-                  PORT_REDIRECT(i);                      // Reply to the serial port that sent the command
+                  PORT_REDIRECT(p);                      // Reply to the serial port that sent the command
                   SERIAL_ECHOLNPGM(STR_ERR_STOPPED);
                   LCD_MESSAGEPGM(MSG_STOPPED);
                   break;
@@ -569,14 +569,14 @@ void GCodeQueue::get_serial_commands() {
           #endif
 
           // Add the command to the queue
-          _enqueue(serial_line_buffer[i], true
+          _enqueue(serial_line_buffer[p], true
             #if HAS_MULTI_SERIAL
-              , i
+              , p
             #endif
           );
         }
         else
-          process_stream_char(serial_char, serial_input_state[i], serial_line_buffer[i], serial_count[i]);
+          process_stream_char(serial_char, serial_input_state[p], serial_line_buffer[p], serial_count[p]);
 
       } // char_count loop
 
diff --git a/Marlin/src/gcode/queue.h b/Marlin/src/gcode/queue.h
index 57d4beecb8..d677146a7d 100644
--- a/Marlin/src/gcode/queue.h
+++ b/Marlin/src/gcode/queue.h
@@ -56,12 +56,9 @@ public:
    * The port that the command was received on
    */
   #if HAS_MULTI_SERIAL
-    static int16_t port[BUFSIZE];
+    static serial_index_t port[BUFSIZE];
   #endif
-
-  static int16_t command_port() {
-    return TERN0(HAS_MULTI_SERIAL, port[index_r]);
-  }
+  static inline serial_index_t command_port() { return TERN0(HAS_MULTI_SERIAL, port[index_r]); }
 
   GCodeQueue();
 
@@ -159,13 +156,13 @@ private:
 
   static void _commit_command(bool say_ok
     #if HAS_MULTI_SERIAL
-      , int16_t p=-1
+      , serial_index_t serial_ind=-1
     #endif
   );
 
   static bool _enqueue(const char* cmd, bool say_ok=false
     #if HAS_MULTI_SERIAL
-      , int16_t p=-1
+      , serial_index_t serial_ind=-1
     #endif
   );
 
@@ -181,7 +178,7 @@ private:
    */
   static bool enqueue_one(const char* cmd);
 
-  static void gcode_line_error(PGM_P const err, const int8_t pn);
+  static void gcode_line_error(PGM_P const err, const serial_index_t serial_ind);
 
 };
 
diff --git a/Marlin/src/sd/cardreader.cpp b/Marlin/src/sd/cardreader.cpp
index 307f31e431..2e9101ff84 100644
--- a/Marlin/src/sd/cardreader.cpp
+++ b/Marlin/src/sd/cardreader.cpp
@@ -1229,7 +1229,7 @@ void CardReader::fileHasFinished() {
   uint8_t CardReader::auto_report_sd_interval = 0;
   millis_t CardReader::next_sd_report_ms;
   #if HAS_MULTI_SERIAL
-    int8_t CardReader::auto_report_port;
+    serial_index_t CardReader::auto_report_port;
   #endif
 
   void CardReader::auto_report_sd_status() {
diff --git a/Marlin/src/sd/cardreader.h b/Marlin/src/sd/cardreader.h
index 7a312b1b57..272e213800 100644
--- a/Marlin/src/sd/cardreader.h
+++ b/Marlin/src/sd/cardreader.h
@@ -267,7 +267,7 @@ private:
     static uint8_t auto_report_sd_interval;
     static millis_t next_sd_report_ms;
     #if HAS_MULTI_SERIAL
-      static int8_t auto_report_port;
+      static serial_index_t auto_report_port;
     #endif
   #endif