diff --git a/Marlin/src/HAL/HAL_STM32F1/HAL_Servo_STM32F1.cpp b/Marlin/src/HAL/HAL_STM32F1/HAL_Servo_STM32F1.cpp
index f8fc315ba..ef81db69f 100644
--- a/Marlin/src/HAL/HAL_STM32F1/HAL_Servo_STM32F1.cpp
+++ b/Marlin/src/HAL/HAL_STM32F1/HAL_Servo_STM32F1.cpp
@@ -27,7 +27,7 @@
 
 #if HAS_SERVOS
 
-uint8_t ServoCount; //=0
+uint8_t ServoCount = 0;
 
 #include "HAL_Servo_STM32F1.h"
 
@@ -68,16 +68,16 @@ libServo::libServo() {
 
 bool libServo::attach(const int32_t pin, const int32_t minAngle, const int32_t maxAngle) {
   if (this->servoIndex >= MAX_SERVOS) return false;
+  if (!PWM_PIN(pin)) return false;
 
-  this->pin = pin;
   this->minAngle = minAngle;
   this->maxAngle = maxAngle;
 
-  timer_dev *tdev = PIN_MAP[this->pin].timer_device;
-  uint8_t tchan = PIN_MAP[this->pin].timer_channel;
+  timer_dev *tdev = PIN_MAP[pin].timer_device;
+  uint8_t tchan = PIN_MAP[pin].timer_channel;
 
-  pinMode(this->pin, PWM);
-  pwmWrite(this->pin, 0);
+  pinMode(pin, PWM);
+  pwmWrite(pin, 0);
 
   timer_pause(tdev);
   timer_set_prescaler(tdev, SERVO_PRESCALER - 1); // prescaler is 1-based
@@ -85,6 +85,8 @@ bool libServo::attach(const int32_t pin, const int32_t minAngle, const int32_t m
   timer_generate_update(tdev);
   timer_resume(tdev);
 
+  this->pin = pin; // set attached()
+
   return true;
 }
 
diff --git a/Marlin/src/HAL/HAL_STM32F1/fastio_STM32F1.h b/Marlin/src/HAL/HAL_STM32F1/fastio_STM32F1.h
index 3ca2dfdd9..ad225a8f9 100644
--- a/Marlin/src/HAL/HAL_STM32F1/fastio_STM32F1.h
+++ b/Marlin/src/HAL/HAL_STM32F1/fastio_STM32F1.h
@@ -51,7 +51,7 @@
 #define IS_INPUT(IO)          (_GET_MODE(IO) == GPIO_INPUT_FLOATING || _GET_MODE(IO) == GPIO_INPUT_ANALOG || _GET_MODE(IO) == GPIO_INPUT_PU || _GET_MODE(IO) == GPIO_INPUT_PD)
 #define IS_OUTPUT(IO)         (_GET_MODE(IO) == GPIO_OUTPUT_PP)
 
-#define PWM_PIN(P)            (PIN_MAP[IO].timer_device != nullptr)
+#define PWM_PIN(IO)           (PIN_MAP[IO].timer_device != nullptr)
 
 // digitalRead/Write wrappers
 #define extDigitalRead(IO)    digitalRead(IO)
diff --git a/Marlin/src/gcode/control/M280.cpp b/Marlin/src/gcode/control/M280.cpp
index e7ee35413..f973e81b1 100644
--- a/Marlin/src/gcode/control/M280.cpp
+++ b/Marlin/src/gcode/control/M280.cpp
@@ -34,8 +34,13 @@ void GcodeSuite::M280() {
   if (!parser.seen('P')) return;
   const int servo_index = parser.value_int();
   if (WITHIN(servo_index, 0, NUM_SERVOS - 1)) {
-    if (parser.seen('S'))
-      MOVE_SERVO(servo_index, parser.value_int());
+    if (parser.seen('S')) {
+      const int a = parser.value_int();
+      if (a == -1)
+        servo[servo_index].detach();
+      else
+        MOVE_SERVO(servo_index, a);
+    }
     else {
       SERIAL_ECHO_START();
       SERIAL_ECHOPAIR(" Servo ", servo_index);