diff --git a/Marlin/src/Marlin.cpp b/Marlin/src/Marlin.cpp
index f83935698f..9c071c0a57 100644
--- a/Marlin/src/Marlin.cpp
+++ b/Marlin/src/Marlin.cpp
@@ -357,10 +357,6 @@ void suicide() {
  ***************** GCode Handlers *****************
  **************************************************/
 
-#if ENABLED(INCH_MODE_SUPPORT)
-  #include "gcode/units/G20_G21.h"
-#endif
-
 #if ENABLED(NOZZLE_PARK_FEATURE)
   #include "gcode/feature/pause/G27.h"
 #endif
diff --git a/Marlin/src/gcode/gcode.cpp b/Marlin/src/gcode/gcode.cpp
index 1577defd35..5df697a760 100644
--- a/Marlin/src/gcode/gcode.cpp
+++ b/Marlin/src/gcode/gcode.cpp
@@ -116,8 +116,6 @@ void GcodeSuite::dwell(millis_t time) {
 //
 // Placeholders for non-migrated codes
 //
-extern void gcode_G20();
-extern void gcode_G21();
 extern void gcode_G27();
 extern void gcode_G30();
 extern void gcode_G31();
@@ -331,11 +329,11 @@ void GcodeSuite::process_next_command() {
 
       #if ENABLED(INCH_MODE_SUPPORT)
         case 20: // G20: Inch Mode
-          gcode_G20();
+          G20();
           break;
 
         case 21: // G21: MM Mode
-          gcode_G21();
+          G21();
           break;
       #endif // INCH_MODE_SUPPORT
 
diff --git a/Marlin/src/gcode/units/G20_G21.h b/Marlin/src/gcode/units/G20_G21.cpp
similarity index 77%
rename from Marlin/src/gcode/units/G20_G21.h
rename to Marlin/src/gcode/units/G20_G21.cpp
index 6f57f04d28..74ff343af5 100644
--- a/Marlin/src/gcode/units/G20_G21.h
+++ b/Marlin/src/gcode/units/G20_G21.cpp
@@ -20,12 +20,20 @@
  *
  */
 
+#include "../../inc/MarlinConfig.h"
+
+#if ENABLED(INCH_MODE_SUPPORT)
+
+#include "../gcode.h"
+
 /**
  * G20: Set input mode to inches
  */
-void gcode_G20() { parser.set_input_linear_units(LINEARUNIT_INCH); }
+void GcodeSuite::G20() { parser.set_input_linear_units(LINEARUNIT_INCH); }
 
 /**
  * G21: Set input mode to millimeters
  */
-void gcode_G21() { parser.set_input_linear_units(LINEARUNIT_MM); }
+void GcodeSuite::G21() { parser.set_input_linear_units(LINEARUNIT_MM); }
+
+#endif // INCH_MODE_SUPPORT