diff --git a/Marlin/src/gcode/temp/M306.cpp b/Marlin/src/gcode/temp/M306.cpp
index 4286b2017e..7978922ff4 100644
--- a/Marlin/src/gcode/temp/M306.cpp
+++ b/Marlin/src/gcode/temp/M306.cpp
@@ -74,7 +74,7 @@ void GcodeSuite::M306_report(const bool forReplay/*=true*/) {
     #if ENABLED(MPC_INCLUDE_FAN)
       SERIAL_ECHOPAIR_F(" F", constants.ambient_xfer_coeff_fan0 + constants.fan255_adjustment, 4);
     #endif
-    SERIAL_ECHOPAIR_F(" M", constants.filament_heat_capacity_permm, 4);
+    SERIAL_ECHOPAIR_F(" H", constants.filament_heat_capacity_permm, 4);
     SERIAL_EOL();
   }
 }
diff --git a/Marlin/src/module/temperature.h b/Marlin/src/module/temperature.h
index da9d4a071b..c11c9d76de 100644
--- a/Marlin/src/module/temperature.h
+++ b/Marlin/src/module/temperature.h
@@ -103,7 +103,7 @@ hotend_pid_t;
     #if ENABLED(MPC_INCLUDE_FAN)
       float fan255_adjustment;          // M306 F
     #endif
-    float filament_heat_capacity_permm; // M306 M
+    float filament_heat_capacity_permm; // M306 H
   } MPC_t;
 #endif