diff --git a/Marlin/src/gcode/calibrate/M100.cpp b/Marlin/src/gcode/calibrate/M100.cpp
index a6f4f8f5d2e70c8cad1d9873d17a9bcefe7cb991..452dfd033c570d0b30d1cefb81789d66382dace1 100644
--- a/Marlin/src/gcode/calibrate/M100.cpp
+++ b/Marlin/src/gcode/calibrate/M100.cpp
@@ -51,7 +51,7 @@
  * Also, there are two support functions that can be called from a developer's C code.
  *
  *    uint16_t check_for_free_memory_corruption(PGM_P const free_memory_start);
- *    void M100_dump_routine(PGM_P const title, char *start, char *end);
+ *    void M100_dump_routine(PGM_P const title, const char * const start, const char * const end);
  *
  * Initial version by Roxy-3D
  */
@@ -151,8 +151,8 @@ inline int32_t count_test_bytes(const char * const start_free_memory) {
     // Start and end the dump on a nice 16 byte boundary
     // (even though the values are not 16-byte aligned).
     //
-    start_free_memory = (char*)((ptr_int_t)((uint32_t)start_free_memory & 0xFFFFFFF0)); // Align to 16-byte boundary
-    end_free_memory  = (char*)((ptr_int_t)((uint32_t)end_free_memory  | 0x0000000F)); // Align end_free_memory to the 15th byte (at or above end_free_memory)
+    start_free_memory = (char*)(ptr_int_t(uint32_t(start_free_memory) & ~0xFUL)); // Align to 16-byte boundary
+    end_free_memory   = (char*)(ptr_int_t(uint32_t(end_free_memory)   |  0xFUL)); // Align end_free_memory to the 15th byte (at or above end_free_memory)
 
     // Dump command main loop
     while (start_free_memory < end_free_memory) {
@@ -177,15 +177,16 @@ inline int32_t count_test_bytes(const char * const start_free_memory) {
     }
   }
 
-  void M100_dump_routine(PGM_P const title, char *start, char *end) {
+  void M100_dump_routine(PGM_P const title, const char * const start, const char * const end) {
     serialprintPGM(title);
     SERIAL_EOL();
     //
     // Round the start and end locations to produce full lines of output
     //
-    start = (char*)((ptr_int_t)((uint32_t)start & 0xFFFFFFF0)); // Align to 16-byte boundary
-    end   = (char*)((ptr_int_t)((uint32_t)end   | 0x0000000F)); // Align end_free_memory to the 15th byte (at or above end_free_memory)
-    dump_free_memory(start, end);
+    dump_free_memory(
+      (char*)(ptr_int_t(uint32_t(start) & ~0xFUL)), // Align to 16-byte boundary
+      (char*)(ptr_int_t(uint32_t(end)   |  0xFUL))  // Align end_free_memory to the 15th byte (at or above end_free_memory)
+    );
   }
 
 #endif // M100_FREE_MEMORY_DUMPER
@@ -211,7 +212,7 @@ inline int check_for_free_memory_corruption(PGM_P const title) {
     //   idle();
     serial_delay(20);
     #if ENABLED(M100_FREE_MEMORY_DUMPER)
-      M100_dump_routine(PSTR("   Memory corruption detected with end_free_memory<Heap\n"), (char*)0x1B80, (char*)0x21FF);
+      M100_dump_routine(PSTR("   Memory corruption detected with end_free_memory<Heap\n"), (const char*)0x1B80, (const char*)0x21FF);
     #endif
   }
 
diff --git a/Marlin/src/gcode/gcode.cpp b/Marlin/src/gcode/gcode.cpp
index 92928cf8b3350c1edc592c857e6c9ce89a15142a..d835ce65558ecfbedb98e0e2c533d0bef5282e45 100644
--- a/Marlin/src/gcode/gcode.cpp
+++ b/Marlin/src/gcode/gcode.cpp
@@ -209,7 +209,7 @@ void GcodeSuite::dwell(millis_t time) {
 // Placeholders for non-migrated codes
 //
 #if ENABLED(M100_FREE_MEMORY_WATCHER)
-  extern void M100_dump_routine(PGM_P const title, char *start, char *end);
+  extern void M100_dump_routine(PGM_P const title, const char * const start, const char * const end);
 #endif
 
 /**
@@ -865,7 +865,7 @@ void GcodeSuite::process_next_command() {
     SERIAL_ECHOLN(current_command);
     #if ENABLED(M100_FREE_MEMORY_DUMPER)
       SERIAL_ECHOPAIR("slot:", queue.index_r);
-      M100_dump_routine(PSTR("   Command Queue:"), queue.command_buffer, queue.command_buffer + sizeof(queue.command_buffer));
+      M100_dump_routine(PSTR("   Command Queue:"), &queue.command_buffer[0][0], &queue.command_buffer[BUFSIZE - 1][MAX_CMD_SIZE - 1]);
     #endif
   }