diff --git a/Marlin/src/core/serial.h b/Marlin/src/core/serial.h
index f76f0e32f..57e9636be 100644
--- a/Marlin/src/core/serial.h
+++ b/Marlin/src/core/serial.h
@@ -62,37 +62,36 @@ extern uint8_t marlin_debug_flags;
 //
 // Serial redirection
 //
-#define SERIAL_ALL 0xFF
 #if HAS_MULTI_SERIAL
-  #define _PORT_REDIRECT(n,p)   REMEMBER(n,multiSerial.portMask,p)
-  #define _PORT_RESTORE(n,p)    RESTORE(n)
-  #define SERIAL_ASSERT(P)      if(multiSerial.portMask!=(P)){ debugger(); }
+  #define _PORT_REDIRECT(n,p) REMEMBER(n,multiSerial.portMask,p)
+  #define _PORT_RESTORE(n,p)  RESTORE(n)
+  #define SERIAL_ASSERT(P)    if(multiSerial.portMask!=(P)){ debugger(); }
   #ifdef SERIAL_CATCHALL
     typedef MultiSerial<decltype(MYSERIAL), decltype(SERIAL_CATCHALL), 0> SerialOutputT;
   #else
-    typedef MultiSerial<decltype(MYSERIAL0), TERN(HAS_ETHERNET, ConditionalSerial<decltype(MYSERIAL1)>, decltype(MYSERIAL1)), 0>      SerialOutputT;
+    typedef MultiSerial<decltype(MYSERIAL0), TERN(HAS_ETHERNET, ConditionalSerial<decltype(MYSERIAL1)>, decltype(MYSERIAL1)), 0> SerialOutputT;
   #endif
-  extern SerialOutputT          multiSerial;
-  #define _SERIAL_IMPL          multiSerial
+  extern SerialOutputT        multiSerial;
+  #define _SERIAL_IMPL        multiSerial
 #else
-  #define _PORT_REDIRECT(n,p)   NOOP
-  #define _PORT_RESTORE(n)      NOOP
-  #define SERIAL_ASSERT(P)      NOOP
-  #define _SERIAL_IMPL          MYSERIAL0
+  #define _PORT_REDIRECT(n,p) NOOP
+  #define _PORT_RESTORE(n)    NOOP
+  #define SERIAL_ASSERT(P)    NOOP
+  #define _SERIAL_IMPL        MYSERIAL0
 #endif
 
 #if ENABLED(MEATPACK)
   extern MeatpackSerial<decltype(_SERIAL_IMPL)> mpSerial;
-  #define SERIAL_IMPL          mpSerial
+  #define SERIAL_IMPL mpSerial
 #else
-  #define SERIAL_IMPL          _SERIAL_IMPL
+  #define SERIAL_IMPL _SERIAL_IMPL
 #endif
 
 #define SERIAL_OUT(WHAT, V...)  (void)SERIAL_IMPL.WHAT(V)
 
-#define PORT_REDIRECT(p)        _PORT_REDIRECT(1,p)
-#define PORT_RESTORE()          _PORT_RESTORE(1)
-#define SERIAL_PORTMASK(P)      _BV(P)
+#define PORT_REDIRECT(p)   _PORT_REDIRECT(1,p)
+#define PORT_RESTORE()     _PORT_RESTORE(1)
+#define SERIAL_PORTMASK(P) SerialMask::from(P)
 
 //
 // SERIAL_CHAR - Print one or more individual chars
diff --git a/Marlin/src/core/serial_base.h b/Marlin/src/core/serial_base.h
index 418bb557e..f8fe3a181 100644
--- a/Marlin/src/core/serial_base.h
+++ b/Marlin/src/core/serial_base.h
@@ -22,12 +22,29 @@
 #pragma once
 
 #include "../inc/MarlinConfigPre.h"
-#include "macros.h"
 
 #if ENABLED(EMERGENCY_PARSER)
   #include "../feature/e_parser.h"
 #endif
 
+// Used in multiple places
+// You can build it but not manipulate it.
+// There are only few places where it's required to access the underlying member: GCodeQueue, SerialMask and MultiSerial
+struct serial_index_t {
+  // A signed index, where -1 is a special case meaning no action (neither output or input)
+  int8_t  index;
+
+  // Check if the index is within the range [a ... b]
+  constexpr inline bool within(const int8_t a, const int8_t b) const { return WITHIN(index, a, b); }
+  constexpr inline bool valid() const { return WITHIN(index, 0, 7); } // At most, 8 bits
+
+  // Construction is either from an index
+  constexpr serial_index_t(const int8_t index) : index(index) {}
+
+  // Default to "no index"
+  constexpr serial_index_t() : index(-1) {}
+};
+
 // flushTX is not implemented in all HAL, so use SFINAE to call the method where it is.
 CALL_IF_EXISTS_IMPL(void, flushTX);
 CALL_IF_EXISTS_IMPL(bool, connected, true);
@@ -79,10 +96,10 @@ struct SerialBase {
   void end()                        { static_cast<Child*>(this)->end(); }
   /** Check for available data from the port
       @param index  The port index, usually 0 */
-  int available(uint8_t index = 0)  { return static_cast<Child*>(this)->available(index); }
+  int available(serial_index_t index = 0)  { return static_cast<Child*>(this)->available(index); }
   /** Read a value from the port
       @param index  The port index, usually 0 */
-  int  read(uint8_t index = 0)      { return static_cast<Child*>(this)->read(index); }
+  int  read(serial_index_t index = 0)      { return static_cast<Child*>(this)->read(index); }
   // Check if the serial port is connected (usually bypassed)
   bool connected()                  { return static_cast<Child*>(this)->connected(); }
   // Redirect flush
diff --git a/Marlin/src/core/serial_hook.h b/Marlin/src/core/serial_hook.h
index dc2da1350..5e81e9e0e 100644
--- a/Marlin/src/core/serial_hook.h
+++ b/Marlin/src/core/serial_hook.h
@@ -21,11 +21,32 @@
  */
 #pragma once
 
-#include "macros.h"
 #include "serial_base.h"
 
-// Used in multiple places
-typedef int8_t serial_index_t;
+// A mask containing a bitmap of the serial port to act upon
+// This is written to ensure a serial index is never used as a serial mask
+class SerialMask {
+  uint8_t mask;
+
+  // This constructor is private to ensure you can't convert an index to a mask
+  // The compiler will stop here if you are mixing index and mask in your code.
+  // If you need to, you'll have to use the explicit static "from" method here
+  SerialMask(const serial_index_t);
+
+public:
+  inline constexpr bool enabled(const SerialMask PortMask) const    { return mask & PortMask.mask; }
+  inline constexpr SerialMask combine(const SerialMask other) const { return SerialMask(mask | other.mask); }
+  inline constexpr SerialMask operator<< (const int offset) const   { return SerialMask(mask << offset); }
+  static inline SerialMask from(const serial_index_t index) {
+    if (index.valid()) return SerialMask(_BV(index.index));
+    return SerialMask(0); // A invalid index mean no output
+  }
+
+  constexpr SerialMask(const uint8_t mask) : mask(mask) {}
+  constexpr SerialMask(const SerialMask & other) : mask(other.mask) {} // Can't use = default here since not all framework support this
+
+  static constexpr uint8_t All = 0xFF;
+};
 
 // The most basic serial class: it dispatch to the base serial class with no hook whatsoever. This will compile to nothing but the base serial class
 template <class SerialT>
@@ -39,10 +60,10 @@ struct BaseSerial : public SerialBase< BaseSerial<SerialT> >, public SerialT {
   void msgDone() {}
 
   // We don't care about indices here, since if one can call us, it's the right index anyway
-  int available(uint8_t)  { return (int)SerialT::available(); }
-  int read(uint8_t)       { return (int)SerialT::read(); }
-  bool connected()        { return CALL_IF_EXISTS(bool, static_cast<SerialT*>(this), connected);; }
-  void flushTX()          { CALL_IF_EXISTS(void, static_cast<SerialT*>(this), flushTX); }
+  int available(serial_index_t) { return (int)SerialT::available(); }
+  int read(serial_index_t)      { return (int)SerialT::read(); }
+  bool connected()              { return CALL_IF_EXISTS(bool, static_cast<SerialT*>(this), connected);; }
+  void flushTX()                { CALL_IF_EXISTS(void, static_cast<SerialT*>(this), flushTX); }
 
   // We have 2 implementation of the same method in both base class, let's say which one we want
   using SerialT::available;
@@ -77,11 +98,10 @@ struct ConditionalSerial : public SerialBase< ConditionalSerial<SerialT> > {
   bool connected()          { return CALL_IF_EXISTS(bool, &out, connected); }
   void flushTX()            { CALL_IF_EXISTS(void, &out, flushTX); }
 
-  int available(uint8_t )   { return (int)out.available(); }
-  int read(uint8_t )        { return (int)out.read(); }
-  int available()           { return (int)out.available(); }
-  int read()                { return (int)out.read(); }
-
+  int available(serial_index_t )  { return (int)out.available(); }
+  int read(serial_index_t )       { return (int)out.read(); }
+  int available()                 { return (int)out.available(); }
+  int read()                      { return (int)out.read(); }
 
   ConditionalSerial(bool & conditionVariable, SerialT & out, const bool e) : BaseClassT(e), condition(conditionVariable), out(out) {}
 };
@@ -102,8 +122,8 @@ struct ForwardSerial : public SerialBase< ForwardSerial<SerialT> > {
   bool connected()              { return Private::HasMember_connected<SerialT>::value ? CALL_IF_EXISTS(bool, &out, connected) : (bool)out; }
   void flushTX()                { CALL_IF_EXISTS(void, &out, flushTX); }
 
-  int available(uint8_t)        { return (int)out.available(); }
-  int read(uint8_t)             { return (int)out.read(); }
+  int available(serial_index_t) { return (int)out.available(); }
+  int read(serial_index_t)      { return (int)out.read(); }
   int available()               { return (int)out.available(); }
   int read()                    { return (int)out.read(); }
 
@@ -130,8 +150,8 @@ struct RuntimeSerial : public SerialBase< RuntimeSerial<SerialT> >, public Seria
     if (eofHook) eofHook(userPointer);
   }
 
-  int available(uint8_t)  { return (int)SerialT::available(); }
-  int read(uint8_t)       { return (int)SerialT::read(); }
+  int available(serial_index_t)  { return (int)SerialT::available(); }
+  int read(serial_index_t)       { return (int)SerialT::read(); }
   using SerialT::available;
   using SerialT::read;
   using SerialT::flush;
@@ -170,53 +190,51 @@ template <class Serial0T, class Serial1T, const uint8_t offset = 0, const uint8_
 struct MultiSerial : public SerialBase< MultiSerial<Serial0T, Serial1T, offset, step> > {
   typedef SerialBase< MultiSerial<Serial0T, Serial1T, offset, step> > BaseClassT;
 
-  uint8_t    portMask;
+  SerialMask portMask;
   Serial0T & serial0;
   Serial1T & serial1;
 
-  enum Masks {
-    UsageMask         =  ((1 << step) - 1), // A bit mask containing as many bits as step
-    FirstOutputMask   =  (UsageMask << offset),
-    SecondOutputMask  =  (UsageMask << (offset + step)),
-    AllMask           = FirstOutputMask | SecondOutputMask,
-  };
+  static constexpr uint8_t Usage         =  ((1 << step) - 1); // A bit mask containing as many bits as step
+  static constexpr uint8_t FirstOutput   = (Usage << offset);
+  static constexpr uint8_t SecondOutput  = (Usage << (offset + step));
+  static constexpr uint8_t Both          = FirstOutput | SecondOutput;
 
   NO_INLINE size_t write(uint8_t c) {
     size_t ret = 0;
-    if (portMask & FirstOutputMask)   ret = serial0.write(c);
-    if (portMask & SecondOutputMask)  ret = serial1.write(c) | ret;
+    if (portMask.enabled(FirstOutput))   ret = serial0.write(c);
+    if (portMask.enabled(SecondOutput))  ret = serial1.write(c) | ret;
     return ret;
   }
   NO_INLINE void msgDone() {
-    if (portMask & FirstOutputMask)   serial0.msgDone();
-    if (portMask & SecondOutputMask)  serial1.msgDone();
+    if (portMask.enabled(FirstOutput))   serial0.msgDone();
+    if (portMask.enabled(SecondOutput))  serial1.msgDone();
   }
-  int available(uint8_t index) {
-    if (index >= 0 + offset && index < step + offset)
+  int available(serial_index_t index) {
+    if (index.within(0 + offset, step + offset - 1))
       return serial0.available(index);
-    else if (index >= step + offset && index < 2 * step + offset)
+    else if (index.within(step + offset, 2 * step + offset - 1))
       return serial1.available(index);
     return false;
   }
-  int read(uint8_t index) {
-    if (index >= 0 + offset && index < step + offset)
+  int read(serial_index_t index) {
+    if (index.within(0 + offset, step + offset - 1))
       return serial0.read(index);
-    else if (index >= step + offset && index < 2 * step + offset)
+    else if (index.within(step + offset, 2 * step + offset - 1))
       return serial1.read(index);
     return -1;
   }
   void begin(const long br) {
-    if (portMask & FirstOutputMask)   serial0.begin(br);
-    if (portMask & SecondOutputMask)  serial1.begin(br);
+    if (portMask.enabled(FirstOutput))   serial0.begin(br);
+    if (portMask.enabled(SecondOutput))  serial1.begin(br);
   }
   void end() {
-    if (portMask & FirstOutputMask)   serial0.end();
-    if (portMask & SecondOutputMask)  serial1.end();
+    if (portMask.enabled(FirstOutput))   serial0.end();
+    if (portMask.enabled(SecondOutput))  serial1.end();
   }
   bool connected() {
     bool ret = true;
-    if (portMask & FirstOutputMask)   ret = CALL_IF_EXISTS(bool, &serial0, connected);
-    if (portMask & SecondOutputMask)  ret = ret && CALL_IF_EXISTS(bool, &serial1, connected);
+    if (portMask.enabled(FirstOutput))   ret = CALL_IF_EXISTS(bool, &serial0, connected);
+    if (portMask.enabled(SecondOutput))  ret = ret && CALL_IF_EXISTS(bool, &serial1, connected);
     return ret;
   }
 
@@ -225,15 +243,15 @@ struct MultiSerial : public SerialBase< MultiSerial<Serial0T, Serial1T, offset,
 
   // Redirect flush
   NO_INLINE void flush()      {
-    if (portMask & FirstOutputMask)   serial0.flush();
-    if (portMask & SecondOutputMask)  serial1.flush();
+    if (portMask.enabled(FirstOutput))   serial0.flush();
+    if (portMask.enabled(SecondOutput))  serial1.flush();
   }
   NO_INLINE void flushTX()    {
-    if (portMask & FirstOutputMask)   CALL_IF_EXISTS(void, &serial0, flushTX);
-    if (portMask & SecondOutputMask)  CALL_IF_EXISTS(void, &serial1, flushTX);
+    if (portMask.enabled(FirstOutput))   CALL_IF_EXISTS(void, &serial0, flushTX);
+    if (portMask.enabled(SecondOutput))  CALL_IF_EXISTS(void, &serial1, flushTX);
   }
 
-  MultiSerial(Serial0T & serial0, Serial1T & serial1, int8_t mask = AllMask, const bool e = false) :
+  MultiSerial(Serial0T & serial0, Serial1T & serial1, const SerialMask mask = Both, const bool e = false) :
     BaseClassT(e),
     portMask(mask), serial0(serial0), serial1(serial1) {}
 };
diff --git a/Marlin/src/feature/host_actions.cpp b/Marlin/src/feature/host_actions.cpp
index 2a0b3dc3d..203fdaf53 100644
--- a/Marlin/src/feature/host_actions.cpp
+++ b/Marlin/src/feature/host_actions.cpp
@@ -38,7 +38,7 @@
 #endif
 
 void host_action(PGM_P const pstr, const bool eol) {
-  PORT_REDIRECT(SERIAL_ALL);
+  PORT_REDIRECT(SerialMask::All);
   SERIAL_ECHOPGM("//action:");
   SERIAL_ECHOPGM_P(pstr);
   if (eol) SERIAL_EOL();
@@ -78,19 +78,19 @@ void host_action(PGM_P const pstr, const bool eol) {
   PromptReason host_prompt_reason = PROMPT_NOT_DEFINED;
 
   void host_action_notify(const char * const message) {
-    PORT_REDIRECT(SERIAL_ALL);
+    PORT_REDIRECT(SerialMask::All);
     host_action(PSTR("notification "), false);
     SERIAL_ECHOLN(message);
   }
 
   void host_action_notify_P(PGM_P const message) {
-    PORT_REDIRECT(SERIAL_ALL);
+    PORT_REDIRECT(SerialMask::All);
     host_action(PSTR("notification "), false);
     SERIAL_ECHOLNPGM_P(message);
   }
 
   void host_action_prompt(PGM_P const ptype, const bool eol=true) {
-    PORT_REDIRECT(SERIAL_ALL);
+    PORT_REDIRECT(SerialMask::All);
     host_action(PSTR("prompt_"), false);
     SERIAL_ECHOPGM_P(ptype);
     if (eol) SERIAL_EOL();
@@ -98,7 +98,7 @@ void host_action(PGM_P const pstr, const bool eol) {
 
   void host_action_prompt_plus(PGM_P const ptype, PGM_P const pstr, const char extra_char='\0') {
     host_action_prompt(ptype, false);
-    PORT_REDIRECT(SERIAL_ALL);
+    PORT_REDIRECT(SerialMask::All);
     SERIAL_CHAR(' ');
     SERIAL_ECHOPGM_P(pstr);
     if (extra_char != '\0') SERIAL_CHAR(extra_char);
diff --git a/Marlin/src/feature/meatpack.h b/Marlin/src/feature/meatpack.h
index e30a5ac97..96004cfea 100644
--- a/Marlin/src/feature/meatpack.h
+++ b/Marlin/src/feature/meatpack.h
@@ -132,17 +132,17 @@ struct MeatpackSerial : public SerialBase <MeatpackSerial < SerialT >> {
   uint8_t charCount;
   uint8_t readIndex;
 
-  NO_INLINE size_t write(uint8_t c) { return out.write(c); }
-  void flush()                      { out.flush();  }
-  void begin(long br)               { out.begin(br); readIndex = 0; }
-  void end()                        { out.end(); }
+  NO_INLINE size_t write(uint8_t c)   { return out.write(c); }
+  void flush()                        { out.flush();  }
+  void begin(long br)                 { out.begin(br); readIndex = 0; }
+  void end()                          { out.end(); }
 
-  void msgDone()                    { out.msgDone(); }
+  void msgDone()                      { out.msgDone(); }
   // Existing instances implement Arduino's operator bool, so use that if it's available
-  bool connected()                  { return Private::HasMember_connected<SerialT>::value ? CALL_IF_EXISTS(bool, &out, connected) : (bool)out; }
-  void flushTX()                    { CALL_IF_EXISTS(void, &out, flushTX); }
+  bool connected()                    { return Private::HasMember_connected<SerialT>::value ? CALL_IF_EXISTS(bool, &out, connected) : (bool)out; }
+  void flushTX()                      { CALL_IF_EXISTS(void, &out, flushTX); }
 
-  int available(uint8_t index) {
+  int available(serial_index_t index) {
     // There is a potential issue here with multiserial, since it'll return its decoded buffer whatever the serial index here.
     // So, instead of doing MeatpackSerial<MultiSerial<...>> we should do MultiSerial<MeatpackSerial<...>, MeatpackSerial<...>>
     // TODO, let's fix this later on
@@ -160,7 +160,7 @@ struct MeatpackSerial : public SerialBase <MeatpackSerial < SerialT >> {
     return charCount;
   }
 
-  int readImpl(const uint8_t index) {
+  int readImpl(const serial_index_t index) {
     // Not enough char to make progress?
     if (charCount == 0 && available(index) == 0) return -1;
 
@@ -168,9 +168,9 @@ struct MeatpackSerial : public SerialBase <MeatpackSerial < SerialT >> {
     return serialBuffer[readIndex++];
   }
 
-  int read(uint8_t index) { return readImpl(index); }
-  int available()         { return available(0); }
-  int read()              { return readImpl(0); }
+  int read(serial_index_t index)  { return readImpl(index); }
+  int available()                 { return available(0); }
+  int read()                      { return readImpl(0); }
 
   MeatpackSerial(const bool e, SerialT & out) : BaseClassT(e), out(out) {}
 };
diff --git a/Marlin/src/gcode/gcode.cpp b/Marlin/src/gcode/gcode.cpp
index 5f30064b1..4e324e789 100644
--- a/Marlin/src/gcode/gcode.cpp
+++ b/Marlin/src/gcode/gcode.cpp
@@ -1067,7 +1067,7 @@ void GcodeSuite::process_subcommands_now(char * gcode) {
     static millis_t next_busy_signal_ms = 0;
     if (!autoreport_paused && host_keepalive_interval && busy_state != NOT_BUSY) {
       if (PENDING(ms, next_busy_signal_ms)) return;
-      PORT_REDIRECT(SERIAL_ALL);
+      PORT_REDIRECT(SerialMask::All);
       switch (busy_state) {
         case IN_HANDLER:
         case IN_PROCESS:
diff --git a/Marlin/src/gcode/host/M118.cpp b/Marlin/src/gcode/host/M118.cpp
index 9982492f9..d6e591add 100644
--- a/Marlin/src/gcode/host/M118.cpp
+++ b/Marlin/src/gcode/host/M118.cpp
@@ -52,7 +52,7 @@ void GcodeSuite::M118() {
     while (*p == ' ') ++p;
   }
 
-  PORT_REDIRECT(WITHIN(port, 0, NUM_SERIAL) ? (port ? SERIAL_PORTMASK(port - 1) : SERIAL_ALL) : multiSerial.portMask);
+  PORT_REDIRECT(WITHIN(port, 0, NUM_SERIAL) ? (port ? SERIAL_PORTMASK(port - 1) : SerialMask::All) : multiSerial.portMask);
 
   if (hasE) SERIAL_ECHO_START();
   if (hasA) SERIAL_ECHOPGM("//");
diff --git a/Marlin/src/gcode/queue.cpp b/Marlin/src/gcode/queue.cpp
index 9b69f9f1f..a764d80ec 100644
--- a/Marlin/src/gcode/queue.cpp
+++ b/Marlin/src/gcode/queue.cpp
@@ -240,7 +240,7 @@ void GCodeQueue::RingBuffer::ok_to_send() {
   CommandLine &command = commands[index_r];
   #if HAS_MULTI_SERIAL
     const serial_index_t serial_ind = command.port;
-    if (serial_ind < 0) return;
+    if (!serial_ind.valid()) return;              // Optimization here, skip processing if it's not going anywhere
     PORT_REDIRECT(SERIAL_PORTMASK(serial_ind));   // Reply to the serial port that sent the command
   #endif
   if (command.skip_ok) return;
@@ -264,15 +264,15 @@ void GCodeQueue::RingBuffer::ok_to_send() {
  */
 void GCodeQueue::flush_and_request_resend(const serial_index_t serial_ind) {
   #if HAS_MULTI_SERIAL
-    if (serial_ind < 0) return;                   // Never mind. Command came from SD or Flash Drive
+    if (!serial_ind.valid()) return;              // Optimization here, skip if the command came from SD or Flash Drive
     PORT_REDIRECT(SERIAL_PORTMASK(serial_ind));   // Reply to the serial port that sent the command
   #endif
   SERIAL_FLUSH();
   SERIAL_ECHOPGM(STR_RESEND);
-  SERIAL_ECHOLN(serial_state[serial_ind].last_N + 1);
+  SERIAL_ECHOLN(serial_state[serial_ind.index].last_N + 1);
 }
 
-inline bool serial_data_available(uint8_t index) {
+inline bool serial_data_available(serial_index_t index) {
   const int a = SERIAL_IMPL.available(index);
   #if BOTH(RX_BUFFER_MONITOR, RX_BUFFER_SIZE)
     if (a > RX_BUFFER_SIZE - 2) {
@@ -290,15 +290,15 @@ inline bool any_serial_data_available() {
       return true;
 }
 
-inline int read_serial(const uint8_t index) { return SERIAL_IMPL.read(index); }
+inline int read_serial(const serial_index_t index) { return SERIAL_IMPL.read(index); }
 
 void GCodeQueue::gcode_line_error(PGM_P const err, const serial_index_t serial_ind) {
   PORT_REDIRECT(SERIAL_PORTMASK(serial_ind)); // Reply to the serial port that sent the command
   SERIAL_ERROR_START();
-  SERIAL_ECHOLNPAIR_P(err, serial_state[serial_ind].last_N);
+  SERIAL_ECHOLNPAIR_P(err, serial_state[serial_ind.index].last_N);
   while (read_serial(serial_ind) != -1) { /* nada */ } // Clear out the RX buffer. Why don't use flush here ?
   flush_and_request_resend(serial_ind);
-  serial_state[serial_ind].count = 0;
+  serial_state[serial_ind.index].count = 0;
 }
 
 FORCE_INLINE bool is_M29(const char * const cmd) {  // matches "M29" & "M29 ", but not "M290", etc
diff --git a/Marlin/src/gcode/queue.h b/Marlin/src/gcode/queue.h
index 4757b8c37..8e87d114e 100644
--- a/Marlin/src/gcode/queue.h
+++ b/Marlin/src/gcode/queue.h
@@ -79,13 +79,13 @@ public:
 
     void commit_command(bool skip_ok
       #if HAS_MULTI_SERIAL
-        , serial_index_t serial_ind=-1
+        , serial_index_t serial_ind = serial_index_t()
       #endif
     );
 
     bool enqueue(const char* cmd, bool skip_ok = true
       #if HAS_MULTI_SERIAL
-        , serial_index_t serial_ind=-1
+        , serial_index_t serial_ind = serial_index_t()
       #endif
     );
 
@@ -197,7 +197,7 @@ public:
   /**
    * (Re)Set the current line number for the last received command
    */
-  static inline void set_current_line_number(long n) { serial_state[ring_buffer.command_port()].last_N = n; }
+  static inline void set_current_line_number(long n) { serial_state[ring_buffer.command_port().index].last_N = n; }
 
 private:
 
diff --git a/Marlin/src/gcode/sd/M1001.cpp b/Marlin/src/gcode/sd/M1001.cpp
index 1cf700ae2..415fbb6fa 100644
--- a/Marlin/src/gcode/sd/M1001.cpp
+++ b/Marlin/src/gcode/sd/M1001.cpp
@@ -82,7 +82,7 @@ void GcodeSuite::M1001() {
 
   // Announce SD file completion
   {
-    PORT_REDIRECT(SERIAL_ALL);
+    PORT_REDIRECT(SerialMask::All);
     SERIAL_ECHOLNPGM(STR_FILE_PRINTED);
   }
 
diff --git a/Marlin/src/lcd/extui/lib/dgus/DGUSScreenHandler.cpp b/Marlin/src/lcd/extui/lib/dgus/DGUSScreenHandler.cpp
index 180c89580..93a7de14a 100644
--- a/Marlin/src/lcd/extui/lib/dgus/DGUSScreenHandler.cpp
+++ b/Marlin/src/lcd/extui/lib/dgus/DGUSScreenHandler.cpp
@@ -395,21 +395,21 @@ void DGUSScreenHandler::HandleTemperatureChanged(DGUS_VP_Variable &var, void *va
     default: return;
     #if HOTENDS >= 1
       case VP_T_E0_Set:
-        NOMORE(newvalue, HEATER_0_MAXTEMP);
+        NOMORE(newvalue, (uint16_t)HEATER_0_MAXTEMP);
         thermalManager.setTargetHotend(newvalue, 0);
         acceptedvalue = thermalManager.degTargetHotend(0);
         break;
     #endif
     #if HOTENDS >= 2
       case VP_T_E1_Set:
-        NOMORE(newvalue, HEATER_1_MAXTEMP);
+        NOMORE(newvalue, (uint16_t)HEATER_1_MAXTEMP);
         thermalManager.setTargetHotend(newvalue, 1);
         acceptedvalue = thermalManager.degTargetHotend(1);
         break;
     #endif
     #if HAS_HEATED_BED
       case VP_T_Bed_Set:
-        NOMORE(newvalue, BED_MAXTEMP);
+        NOMORE(newvalue, (uint16_t)BED_MAXTEMP);
         thermalManager.setTargetBed(newvalue);
         acceptedvalue = thermalManager.degTargetBed();
         break;
diff --git a/Marlin/src/libs/autoreport.h b/Marlin/src/libs/autoreport.h
index 232216578..a6bc5adbf 100644
--- a/Marlin/src/libs/autoreport.h
+++ b/Marlin/src/libs/autoreport.h
@@ -28,8 +28,8 @@ struct AutoReporter {
   millis_t next_report_ms;
   uint8_t report_interval;
   #if HAS_MULTI_SERIAL
-    serial_index_t report_port_mask;
-    AutoReporter() : report_port_mask(SERIAL_ALL) {}
+    SerialMask report_port_mask;
+    AutoReporter() : report_port_mask(SerialMask::All) {}
   #endif
 
   inline void set_interval(uint8_t seconds, const uint8_t limit=60) {
diff --git a/Marlin/src/module/temperature.cpp b/Marlin/src/module/temperature.cpp
index a1d5745de..a000a31de 100644
--- a/Marlin/src/module/temperature.cpp
+++ b/Marlin/src/module/temperature.cpp
@@ -329,7 +329,7 @@ const char str_t_thermal_runaway[] PROGMEM = STR_T_THERMAL_RUNAWAY,
      */
     void Temperature::report_fan_speed(const uint8_t target) {
       if (target >= FAN_COUNT) return;
-      PORT_REDIRECT(SERIAL_ALL);
+      PORT_REDIRECT(SerialMask::All);
       SERIAL_ECHOLNPAIR("M106 P", target, " S", fan_speed[target]);
     }
   #endif
diff --git a/Marlin/src/sd/cardreader.cpp b/Marlin/src/sd/cardreader.cpp
index c973ba594..fac14e72a 100644
--- a/Marlin/src/sd/cardreader.cpp
+++ b/Marlin/src/sd/cardreader.cpp
@@ -549,7 +549,7 @@ void openFailed(const char * const fname) {
 
 void announceOpen(const uint8_t doing, const char * const path) {
   if (doing) {
-    PORT_REDIRECT(SERIAL_ALL);
+    PORT_REDIRECT(SerialMask::All);
     SERIAL_ECHO_START();
     SERIAL_ECHOPGM("Now ");
     SERIAL_ECHOPGM_P(doing == 1 ? PSTR("doing") : PSTR("fresh"));
@@ -615,7 +615,7 @@ void CardReader::openFileRead(char * const path, const uint8_t subcall_type/*=0*
     sdpos = 0;
 
     { // Don't remove this block, as the PORT_REDIRECT is a RAII
-      PORT_REDIRECT(SERIAL_ALL);
+      PORT_REDIRECT(SerialMask::All);
       SERIAL_ECHOLNPAIR(STR_SD_FILE_OPENED, fname, STR_SD_SIZE, filesize);
       SERIAL_ECHOLNPGM(STR_SD_FILE_SELECTED);
     }