diff --git a/Marlin/src/core/serial.h b/Marlin/src/core/serial.h
index 4aae86529..a248014c6 100644
--- a/Marlin/src/core/serial.h
+++ b/Marlin/src/core/serial.h
@@ -42,18 +42,14 @@ enum MarlinDebugFlags : uint8_t {
 extern uint8_t marlin_debug_flags;
 #define DEBUGGING(F) (marlin_debug_flags & (MARLIN_DEBUG_## F))
 
-#if TX_BUFFER_SIZE < 1
-  #define SERIAL_FLUSHTX()
-#endif
-
 #if NUM_SERIAL > 1
   extern int8_t serial_port_index;
   #define _PORT_REDIRECT(n,p)   REMEMBER(n,serial_port_index,p)
   #define _PORT_RESTORE(n)      RESTORE(n)
   #define SERIAL_BOTH 0x7F
   #define SERIAL_OUT(WHAT, ...) do{ \
-    if (!serial_port_index || serial_port_index == SERIAL_BOTH) MYSERIAL0.WHAT(##__VA_ARGS__); \
-    if ( serial_port_index) MYSERIAL1.WHAT(##__VA_ARGS__); \
+    if (!serial_port_index || serial_port_index == SERIAL_BOTH) MYSERIAL0.WHAT(__VA_ARGS__); \
+    if ( serial_port_index) MYSERIAL1.WHAT(__VA_ARGS__); \
   }while(0)
 #else
   #define _PORT_REDIRECT(n,p)   NOOP
@@ -72,8 +68,11 @@ extern uint8_t marlin_debug_flags;
 #define SERIAL_PRINTLN(x,b)     SERIAL_OUT(println, x, b)
 #define SERIAL_PRINTF(args...)  SERIAL_OUT(printf, args)
 #define SERIAL_FLUSH()          SERIAL_OUT(flush)
+
 #if TX_BUFFER_SIZE > 0
   #define SERIAL_FLUSHTX()      SERIAL_OUT(flushTX)
+#else
+  #define SERIAL_FLUSHTX()
 #endif
 
 #define SERIAL_ECHOPGM(x)                   (serialprintPGM(PSTR(x)))
diff --git a/Marlin/src/gcode/sdcard/M20-M30_M32-M34_M524_M928.cpp b/Marlin/src/gcode/sdcard/M20-M30_M32-M34_M524_M928.cpp
index a61db7d2d..f8c35166e 100644
--- a/Marlin/src/gcode/sdcard/M20-M30_M32-M34_M524_M928.cpp
+++ b/Marlin/src/gcode/sdcard/M20-M30_M32-M34_M524_M928.cpp
@@ -51,11 +51,7 @@
  */
 void GcodeSuite::M20() {
   SERIAL_ECHOLNPGM(MSG_BEGIN_FILE_LIST);
-  card.ls(
-    #if NUM_SERIAL > 1
-      command_queue_port[cmd_queue_index_r]
-    #endif
-  );
+  card.ls();
   SERIAL_ECHOLNPGM(MSG_END_FILE_LIST);
 }
 
@@ -160,10 +156,6 @@ void GcodeSuite::M26() {
  *      OR, with 'C' get the current filename.
  */
 void GcodeSuite::M27() {
-  #if NUM_SERIAL > 1
-    const int16_t port = serial_port_index;
-  #endif
-
   if (parser.seen('C')) {
     SERIAL_ECHOPGM("Current file: ");
     card.printFilename();
@@ -171,19 +163,11 @@ void GcodeSuite::M27() {
 
   #if ENABLED(AUTO_REPORT_SD_STATUS)
     else if (parser.seenval('S'))
-      card.set_auto_report_interval(parser.value_byte()
-        #if NUM_SERIAL > 1
-          , port
-        #endif
-      );
+      card.set_auto_report_interval(parser.value_byte());
   #endif
 
   else
-    card.report_status(
-      #if NUM_SERIAL > 1
-        port
-      #endif
-    );
+    card.report_status();
 }
 
 /**
@@ -281,11 +265,7 @@ void GcodeSuite::M32() {
    *   /Miscellaneous/Armchair/Armchair.gcode
    */
   void GcodeSuite::M33() {
-    card.printLongPath(parser.string_arg
-      #if NUM_SERIAL > 1
-        , command_queue_port[cmd_queue_index_r]
-      #endif
-    );
+    card.printLongPath(parser.string_arg);
   }
 
 #endif // LONG_FILENAME_HOST_SUPPORT
diff --git a/Marlin/src/gcode/stats/M31.cpp b/Marlin/src/gcode/stats/M31.cpp
index a9f590f29..1a6d3e8d1 100644
--- a/Marlin/src/gcode/stats/M31.cpp
+++ b/Marlin/src/gcode/stats/M31.cpp
@@ -34,9 +34,6 @@
  * M31: Get the time since the start of SD Print (or last M109)
  */
 void GcodeSuite::M31() {
-  #if NUM_SERIAL > 1
-    const int16_t port = command_queue_port[cmd_queue_index_r];
-  #endif
   char buffer[21];
   duration_t elapsed = print_job_timer.duration();
   elapsed.toString(buffer);
diff --git a/Marlin/src/gcode/temperature/M105.cpp b/Marlin/src/gcode/temperature/M105.cpp
index d28e87ded..ec366b23f 100644
--- a/Marlin/src/gcode/temperature/M105.cpp
+++ b/Marlin/src/gcode/temperature/M105.cpp
@@ -35,17 +35,9 @@ void GcodeSuite::M105() {
   const int8_t target_extruder = get_target_extruder_from_command();
   if (target_extruder < 0) return;
 
-  #if NUM_SERIAL > 1
-    const int16_t port = command_queue_port[cmd_queue_index_r];
-  #endif
-
   #if HAS_TEMP_SENSOR
     SERIAL_ECHOPGM(MSG_OK);
-    thermalManager.print_heater_states(target_extruder
-      #if NUM_SERIAL > 1
-        , port
-      #endif
-    );
+    thermalManager.print_heater_states(target_extruder);
   #else // !HAS_TEMP_SENSOR
     SERIAL_ERROR_MSG(MSG_ERR_NO_THERMISTORS);
   #endif
diff --git a/Marlin/src/module/temperature.cpp b/Marlin/src/module/temperature.cpp
index 8b494811e..7d1264c14 100644
--- a/Marlin/src/module/temperature.cpp
+++ b/Marlin/src/module/temperature.cpp
@@ -2537,9 +2537,6 @@ void Temperature::isr() {
         #if ENABLED(SHOW_TEMP_ADC_VALUES)
           , rawHotendTemp(target_extruder)
         #endif
-        #if NUM_SERIAL > 1
-          , port
-        #endif
       );
     #endif
     #if HAS_HEATED_BED
@@ -2547,9 +2544,6 @@ void Temperature::isr() {
         #if ENABLED(SHOW_TEMP_ADC_VALUES)
           , rawBedTemp()
         #endif
-        #if NUM_SERIAL > 1
-          , port
-        #endif
         , -1 // BED
       );
     #endif
@@ -2566,9 +2560,6 @@ void Temperature::isr() {
         #if ENABLED(SHOW_TEMP_ADC_VALUES)
           , rawHotendTemp(e)
         #endif
-        #if NUM_SERIAL > 1
-          , port
-        #endif
         , e
       );
     #endif