diff --git a/Marlin/src/gcode/feature/advance/M900.cpp b/Marlin/src/gcode/feature/advance/M900.cpp
index a8384108b5..bbba4f246e 100644
--- a/Marlin/src/gcode/feature/advance/M900.cpp
+++ b/Marlin/src/gcode/feature/advance/M900.cpp
@@ -47,41 +47,7 @@ void GcodeSuite::M900() {
     SERIAL_ECHOPGM(" value out of range");
     if (ten) SERIAL_ECHOPGM(" (0-10)");
     SERIAL_ECHOLNPGM(".");
-  }
-
-  if (!parser.seen_any()) {
-
-    #if ENABLED(EXTRA_LIN_ADVANCE_K)
-
-      #if EXTRUDERS < 2
-        SERIAL_ECHOLNPAIR("Advance S", int(new_slot), " K", kref, "(S", int(!new_slot), " K", lref, ")");
-      #else
-        LOOP_L_N(i, EXTRUDERS) {
-          const bool slot = TEST(lin_adv_slot, i);
-          SERIAL_ECHOLNPAIR("Advance T", int(i), " S", int(slot), " K", planner.extruder_advance_K[i],
-                            "(S", int(!slot), " K", other_extruder_advance_K[i], ")");
-          SERIAL_EOL();
-        }
-      #endif
-
-    #else
-
-      SERIAL_ECHO_START();
-      #if EXTRUDERS < 2
-        SERIAL_ECHOLNPAIR("Advance K=", planner.extruder_advance_K[0]);
-      #else
-        SERIAL_ECHOPGM("Advance K");
-        LOOP_L_N(i, EXTRUDERS) {
-          SERIAL_CHAR(' ', '0' + i, ':');
-          SERIAL_ECHO(planner.extruder_advance_K[i]);
-        }
-        SERIAL_EOL();
-      #endif
-
-    #endif
-
-    return;
-  }
+  };
 
   #if EXTRUDERS < 2
     constexpr uint8_t tool_index = 0;
@@ -93,9 +59,13 @@ void GcodeSuite::M900() {
     }
   #endif
 
-  float &kref = planner.extruder_advance_K[tool_index],
-        &lref = other_extruder_advance_K[tool_index];
-  const float oldK = kref, oldOther = lref;
+  float &kref = planner.extruder_advance_K[tool_index];
+
+  #if ENABLED(EXTRA_LIN_ADVANCE_K)
+    float &lref = other_extruder_advance_K[tool_index];
+  #endif
+
+  const float oldK = kref;
   float newK = oldK;
 
   #if ENABLED(EXTRA_LIN_ADVANCE_K)
@@ -107,32 +77,32 @@ void GcodeSuite::M900() {
     // saved K values. Do here so K/L will apply correctly.
     if (new_slot != old_slot) {                       // Not the same slot?
       SET_BIT_TO(lin_adv_slot, tool_index, new_slot); // Update the slot for the tool
-      newK = oldOther;                                // Get new K value from backup
+      newK = lref;                                    // Get new K value from backup
       lref = oldK;                                    // Save K to backup
     }
 
     // Set the main K value. Apply if the main slot is active.
     if (parser.seenval('K')) {
-      const float newK = parser.value_float();
-      if (!WITHIN(newK, 0, 10)) echo_value_oor('K');
-      else if (new_slot)        lref = newK;          // S1 Knn
-      else                      newK = newK;          // S0 Knn
+      const float K = parser.value_float();
+      if (!WITHIN(K, 0, 10)) echo_value_oor('K');
+      else if (new_slot)        lref = K;             // S1 Knn
+      else                      newK = K;             // S0 Knn
     }
 
     // Set the extra K value. Apply if the extra slot is active.
     if (parser.seenval('L')) {
-      const float newL = parser.value_float();
-      if (!WITHIN(newL, 0, 10)) echo_value_oor('L');
-      else if (!new_slot)       lref = newL;          // S0 Lnn
-      else                      newK = newL;          // S1 Lnn
+      const float L = parser.value_float();
+      if (!WITHIN(L, 0, 10)) echo_value_oor('L');
+      else if (!new_slot)       lref = L;             // S0 Lnn
+      else                      newK = L;             // S1 Lnn
     }
 
   #else
 
     if (parser.seenval('K')) {
-      const float newK = parser.value_float();
-      if (WITHIN(newK, 0, 10))
-        newK = newK;
+      const float K = parser.value_float();
+      if (WITHIN(K, 0, 10))
+        newK = K;
       else
         echo_value_oor('K');
     }
@@ -143,6 +113,39 @@ void GcodeSuite::M900() {
     planner.synchronize();
     kref = newK;
   }
+
+  if (!parser.seen_any()) {
+
+    #if ENABLED(EXTRA_LIN_ADVANCE_K)
+
+      #if EXTRUDERS < 2
+        SERIAL_ECHOLNPAIR("Advance S", int(new_slot), " K", kref, "(S", int(!new_slot), " K", lref, ")");
+      #else
+        LOOP_L_N(i, EXTRUDERS) {
+          const bool slot = TEST(lin_adv_slot, i);
+          SERIAL_ECHOLNPAIR("Advance T", int(i), " S", int(slot), " K", planner.extruder_advance_K[i],
+                            "(S", int(!slot), " K", other_extruder_advance_K[i], ")");
+          SERIAL_EOL();
+        }
+      #endif
+
+    #else
+
+      SERIAL_ECHO_START();
+      #if EXTRUDERS < 2
+        SERIAL_ECHOLNPAIR("Advance K=", planner.extruder_advance_K[0]);
+      #else
+        SERIAL_ECHOPGM("Advance K");
+        LOOP_L_N(i, EXTRUDERS) {
+          SERIAL_CHAR(' ', '0' + i, ':');
+          SERIAL_ECHO(planner.extruder_advance_K[i]);
+        }
+        SERIAL_EOL();
+      #endif
+
+    #endif
+  }
+
 }
 
 #endif // LIN_ADVANCE
diff --git a/buildroot/share/tests/mega2560-tests b/buildroot/share/tests/mega2560-tests
index a896c38733..b09560add5 100755
--- a/buildroot/share/tests/mega2560-tests
+++ b/buildroot/share/tests/mega2560-tests
@@ -45,7 +45,7 @@ opt_enable REPRAP_DISCOUNT_SMART_CONTROLLER LCD_PROGRESS_BAR LCD_PROGRESS_BAR_TE
            BACKLASH_COMPENSATION BACKLASH_GCODE BAUD_RATE_GCODE BEZIER_CURVE_SUPPORT \
            FWRETRACT ARC_P_CIRCLES CNC_WORKSPACE_PLANES CNC_COORDINATE_SYSTEMS \
            PSU_CONTROL AUTO_POWER_CONTROL POWER_LOSS_RECOVERY POWER_LOSS_PIN POWER_LOSS_STATE \
-          SLOW_PWM_HEATERS THERMAL_PROTECTION_CHAMBER LIN_ADVANCE \
+          SLOW_PWM_HEATERS THERMAL_PROTECTION_CHAMBER LIN_ADVANCE EXTRA_LIN_ADVANCE_K \
            HOST_ACTION_COMMANDS HOST_PROMPT_SUPPORT PINS_DEBUGGING MAX7219_DEBUG M114_DETAIL
 exec_test $1 $2 "RAMPS | EXTRUDERS 2 | CHAR LCD + SD | FIX Probe | ABL-Linear | Advanced Pause | PLR | LEDs ..."
 
@@ -66,7 +66,7 @@ opt_enable AUTO_BED_LEVELING_UBL RESTORE_LEVELING_AFTER_G28 DEBUG_LEVELING_FEATU
            REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER LIGHTWEIGHT_UI STATUS_MESSAGE_SCROLLING BOOT_MARLIN_LOGO_SMALL \
            SDSUPPORT SDCARD_SORT_ALPHA USB_FLASH_DRIVE_SUPPORT SCROLL_LONG_FILENAMES CANCEL_OBJECTS \
            EEPROM_SETTINGS EEPROM_CHITCHAT GCODE_MACROS CUSTOM_USER_MENUS \
-           MULTI_NOZZLE_DUPLICATION CLASSIC_JERK LIN_ADVANCE QUICK_HOME \
+           MULTI_NOZZLE_DUPLICATION CLASSIC_JERK LIN_ADVANCE EXTRA_LIN_ADVANCE_K QUICK_HOME \
            LCD_SET_PROGRESS_MANUALLY PRINT_PROGRESS_SHOW_DECIMALS SHOW_REMAINING_TIME \
            BABYSTEPPING BABYSTEP_XY NANODLP_Z_SYNC I2C_POSITION_ENCODERS M114_DETAIL
 exec_test $1 $2 "Azteeg X3 Pro | EXTRUDERS 5 | RRDFGSC | UBL | LIN_ADVANCE ..."