diff --git a/src/drivers/px4io/px4io_serial.cpp b/src/drivers/px4io/px4io_serial.cpp
index c05883aeb8..344b1affa3 100644
--- a/src/drivers/px4io/px4io_serial.cpp
+++ b/src/drivers/px4io/px4io_serial.cpp
@@ -116,10 +116,10 @@ private:
 	volatile unsigned	_rx_dma_status;
 
 	/** bus-ownership lock */
-	sem_t			_bus_semaphore;
+	px4_sem_t			_bus_semaphore;
 
 	/** client-waiting lock/signal */
-	sem_t			_completion_semaphore;
+	px4_sem_t			_completion_semaphore;
 
 	/**
 	 * Start the transaction with IO and wait for it to complete.
@@ -177,8 +177,8 @@ PX4IO_serial::PX4IO_serial() :
 	_tx_dma(nullptr),
 	_rx_dma(nullptr),
 	_rx_dma_status(_dma_status_inactive),
-	_bus_semaphore(SEM_INITIALIZER(0)),
-	_completion_semaphore(SEM_INITIALIZER(0)),
+	_bus_semaphore(px4_sem_initIALIZER(0)),
+	_completion_semaphore(px4_sem_initIALIZER(0)),
 	_pc_txns(perf_alloc(PC_ELAPSED, "io_txns     ")),
 	_pc_dmasetup(perf_alloc(PC_ELAPSED,	"io_dmasetup ")),
 	_pc_retries(perf_alloc(PC_COUNT,	"io_retries  ")),
@@ -219,8 +219,8 @@ PX4IO_serial::~PX4IO_serial()
 	stm32_unconfiggpio(PX4IO_SERIAL_RX_GPIO);
 
 	/* and kill our semaphores */
-	sem_destroy(&_completion_semaphore);
-	sem_destroy(&_bus_semaphore);
+	px4_sem_destroy(&_completion_semaphore);
+	px4_sem_destroy(&_bus_semaphore);
 
 	perf_free(_pc_txns);
 	perf_free(_pc_dmasetup);
@@ -280,8 +280,8 @@ PX4IO_serial::init()
 	rCR1 = USART_CR1_RE | USART_CR1_TE | USART_CR1_UE | USART_CR1_IDLEIE;
 
 	/* create semaphores */
-	sem_init(&_completion_semaphore, 0, 0);
-	sem_init(&_bus_semaphore, 0, 1);
+	px4_sem_init(&_completion_semaphore, 0, 0);
+	px4_sem_init(&_bus_semaphore, 0, 1);
 
 
 	/* XXX this could try talking to IO */
@@ -366,7 +366,7 @@ PX4IO_serial::write(unsigned address, void *data, unsigned count)
 		return -EINVAL;
 	}
 
-	sem_wait(&_bus_semaphore);
+	px4_sem_wait(&_bus_semaphore);
 
 	int result;
 
@@ -403,7 +403,7 @@ PX4IO_serial::write(unsigned address, void *data, unsigned count)
 		perf_count(_pc_retries);
 	}
 
-	sem_post(&_bus_semaphore);
+	px4_sem_post(&_bus_semaphore);
 
 	if (result == OK) {
 		result = count;
@@ -423,7 +423,7 @@ PX4IO_serial::read(unsigned address, void *data, unsigned count)
 		return -EINVAL;
 	}
 
-	sem_wait(&_bus_semaphore);
+	px4_sem_wait(&_bus_semaphore);
 
 	int result;
 
@@ -468,7 +468,7 @@ PX4IO_serial::read(unsigned address, void *data, unsigned count)
 		perf_count(_pc_retries);
 	}
 
-	sem_post(&_bus_semaphore);
+	px4_sem_post(&_bus_semaphore);
 
 	if (result == OK) {
 		result = count;
@@ -551,7 +551,7 @@ PX4IO_serial::_wait_complete()
 	int ret;
 
 	for (;;) {
-		ret = sem_timedwait(&_completion_semaphore, &abstime);
+		ret = px4_sem_timedwait(&_completion_semaphore, &abstime);
 
 		if (ret == OK) {
 			/* check for DMA errors */
@@ -627,7 +627,7 @@ PX4IO_serial::_do_rx_dma_callback(unsigned status)
 		rCR3 &= ~(USART_CR3_DMAT | USART_CR3_DMAR);
 
 		/* complete now */
-		sem_post(&_completion_semaphore);
+		px4_sem_post(&_completion_semaphore);
 	}
 }