diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index 497deea5f..74599ccae 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -629,7 +629,7 @@ static bool send_ok[BUFSIZE];
 
 #ifdef CHDK
   millis_t chdkHigh = 0;
-  boolean chdkActive = false;
+  bool chdkActive = false;
 #endif
 
 #if ENABLED(PID_EXTRUSION_SCALING)
@@ -966,7 +966,7 @@ void gcode_line_error(const char* err, bool doFlush = true) {
 
 inline void get_serial_commands() {
   static char serial_line_buffer[MAX_CMD_SIZE];
-  static boolean serial_comment_mode = false;
+  static bool serial_comment_mode = false;
 
   // If the command buffer is empty for too long,
   // send "wait" to indicate Marlin is still waiting.
@@ -1006,7 +1006,7 @@ inline void get_serial_commands() {
 
       if (npos) {
 
-        boolean M110 = strstr_P(command, PSTR("M110")) != NULL;
+        bool M110 = strstr_P(command, PSTR("M110")) != NULL;
 
         if (M110) {
           char* n2pos = strchr(command + 4, 'N');
diff --git a/Marlin/cardreader.cpp b/Marlin/cardreader.cpp
index e79200c2c..c8e94143c 100644
--- a/Marlin/cardreader.cpp
+++ b/Marlin/cardreader.cpp
@@ -81,7 +81,7 @@ void CardReader::lsDive(const char *prepend, SdFile parent, const char * const m
       createFilename(lfilename, p);
 
       // Allocate enough stack space for the full path to a folder, trailing slash, and nul
-      boolean prepend_is_empty = (prepend[0] == '\0');
+      bool prepend_is_empty = (prepend[0] == '\0');
       int len = (prepend_is_empty ? 1 : strlen(prepend)) + strlen(lfilename) + 1 + 1;
       char path[len];
 
diff --git a/Marlin/servo.cpp b/Marlin/servo.cpp
index b5f9ed86d..34f6dbde8 100644
--- a/Marlin/servo.cpp
+++ b/Marlin/servo.cpp
@@ -227,7 +227,7 @@ static void finISR(timer16_Sequence_t timer) {
   #endif
 }
 
-static boolean isTimerActive(timer16_Sequence_t timer) {
+static bool isTimerActive(timer16_Sequence_t timer) {
   // returns true if any servo is active on this timer
   for (uint8_t channel = 0; channel < SERVOS_PER_TIMER; channel++) {
     if (SERVO(timer, channel).Pin.isActive)