diff --git a/src/AccelStepper.cpp b/src/AccelStepper.cpp
index 54535cc..aae6186 100644
--- a/src/AccelStepper.cpp
+++ b/src/AccelStepper.cpp
@@ -38,7 +38,7 @@ void AccelStepper::move(long relative)
 // Implements steps according to the current step interval
 // You must call this at least once per step
 // returns true if a step occurred
-boolean AccelStepper::runSpeed()
+bool AccelStepper::runSpeed()
 {
     // Dont do anything unless we actually have a step interval
     if (!_stepInterval)
@@ -182,7 +182,7 @@ unsigned long AccelStepper::computeNewSpeed()
 // You must call this at least once per step, preferably in your main loop
 // If the motor is in the desired position, the cost is very small
 // returns true if the motor is still running to the target position.
-boolean AccelStepper::run()
+bool AccelStepper::run()
 {
     if (runSpeed())
 	computeNewSpeed();
@@ -643,7 +643,7 @@ void AccelStepper::runToPosition()
 	YIELD; // Let system housekeeping occur
 }
 
-boolean AccelStepper::runSpeedToPosition()
+bool AccelStepper::runSpeedToPosition()
 {
     if (_targetPos == _currentPos)
 	return false;
diff --git a/src/AccelStepper.h b/src/AccelStepper.h
index 42ee37d..a45dc7c 100644
--- a/src/AccelStepper.h
+++ b/src/AccelStepper.h
@@ -414,13 +414,13 @@ class AccelStepper
     /// preferably in your main loop. Note that each call to run() will make at most one step, and then only when a step is due,
     /// based on the current speed and the time since the last step.
     /// \return true if the motor is still running to the target position.
-    boolean run();
+    bool run();
 
     /// Poll the motor and step it if a step is due, implementing a constant
     /// speed as set by the most recent call to setSpeed(). You must call this as
     /// frequently as possible, but at least once per step interval,
     /// \return true if the motor was stepped.
-    boolean runSpeed();
+    bool runSpeed();
 
     /// Sets the maximum permitted speed. The run() function will accelerate
     /// up to the speed set by this function.
@@ -495,7 +495,7 @@ class AccelStepper
     /// speed unless the target position has been reached.
     /// Does not implement accelerations.
     /// \return true if it stepped
-    boolean runSpeedToPosition();
+    bool runSpeedToPosition();
 
     /// Moves the motor (with acceleration/deceleration)
     /// to the new target position and blocks until it is at
@@ -650,7 +650,7 @@ class AccelStepper
 
     /// Current direction motor is spinning in
     /// Protected because some peoples subclasses need it to be so
-    boolean _direction; // 1 == CW
+    bool _direction; // 1 == CW
     
     /// The current interval between steps in microseconds.
     /// 0 means the motor is currently stopped with _speed == 0
diff --git a/src/MultiStepper.cpp b/src/MultiStepper.cpp
index 6a22e11..ae33bcb 100644
--- a/src/MultiStepper.cpp
+++ b/src/MultiStepper.cpp
@@ -11,7 +11,7 @@ MultiStepper::MultiStepper()
 {
 }
 
-boolean MultiStepper::addStepper(AccelStepper& stepper)
+bool MultiStepper::addStepper(AccelStepper& stepper)
 {
     if (_num_steppers >= MULTISTEPPER_MAX_STEPPERS)
 	return false; // No room for more
@@ -49,10 +49,10 @@ void MultiStepper::moveTo(long absolute[])
 }
 
 // Returns true if any motor is still running to the target position.
-boolean MultiStepper::run()
+bool MultiStepper::run()
 {
     uint8_t i;
-    boolean ret = false;
+    bool ret = false;
     for (i = 0; i < _num_steppers; i++)
     {
 	if ( _steppers[i]->distanceToGo() != 0)
diff --git a/src/MultiStepper.h b/src/MultiStepper.h
index d801bb0..c408648 100644
--- a/src/MultiStepper.h
+++ b/src/MultiStepper.h
@@ -40,7 +40,7 @@ class MultiStepper
     /// There is an upper limit of MULTISTEPPER_MAX_STEPPERS = 10 to the number of steppers that can be managed
     /// \param[in] stepper Reference to a stepper to add to the managed list
     /// \return true if successful. false if the number of managed steppers would exceed MULTISTEPPER_MAX_STEPPERS
-    boolean addStepper(AccelStepper& stepper);
+    bool addStepper(AccelStepper& stepper);
 
     /// Set the target positions of all managed steppers 
     /// according to a coordinate array.
@@ -54,7 +54,7 @@ class MultiStepper
     /// Calls runSpeed() on all the managed steppers
     /// that have not acheived their target position.
     /// \return true if any stepper is still in the process of running to its target position.
-    boolean run();
+    bool run();
 
     /// Runs all managed steppers until they acheived their target position.
     /// Blocks until all that position is acheived. If you dont