diff --git a/src/modules/px4iofirmware/mixer.cpp b/src/modules/px4iofirmware/mixer.cpp
index b6ab3f3989..514f73bad5 100644
--- a/src/modules/px4iofirmware/mixer.cpp
+++ b/src/modules/px4iofirmware/mixer.cpp
@@ -66,10 +66,10 @@ extern "C" {
 #define NAN_VALUE	(0.0f/0.0f)
 
 /* current servo arm/disarm state */
-static bool mixer_servos_armed = false;
-static bool should_arm = false;
-static bool should_arm_nothrottle = false;
-static bool should_always_enable_pwm = false;
+static volatile bool mixer_servos_armed = false;
+static volatile bool should_arm = false;
+static volatile bool should_arm_nothrottle = false;
+static volatile bool should_always_enable_pwm = false;
 static volatile bool in_mixer = false;
 
 extern int _sbus_fd;
@@ -82,15 +82,33 @@ enum mixer_source {
 	MIX_FAILSAFE,
 	MIX_OVERRIDE_FMU_OK
 };
-static mixer_source source;
+static volatile mixer_source source;
 
 static int	mixer_callback(uintptr_t handle,
 			       uint8_t control_group,
 			       uint8_t control_index,
 			       float &control);
 
+static int mixer_mix_threadsafe(float *outputs, volatile uint16_t *limits);
+
 static MixerGroup mixer_group(mixer_callback, 0);
 
+int mixer_mix_threadsafe(float *outputs, volatile uint16_t *limits)
+{
+	/* poor mans mutex */
+	if ((r_status_flags & PX4IO_P_STATUS_FLAGS_MIXER_OK) == 0) {
+		return 0;
+	}
+
+	uint16_t mixer_limits = 0;
+	in_mixer = true;
+	int mixcount = mixer_group.mix(&outputs[0], PX4IO_SERVO_COUNT, &mixer_limits);
+	*limits = mixer_limits;
+	in_mixer = false;
+
+	return mixcount;
+}
+
 void
 mixer_tick(void)
 {
@@ -255,10 +273,7 @@ mixer_tick(void)
 		}
 
 		/* mix */
-		/* poor mans mutex */
-		in_mixer = true;
-		mixed = mixer_group.mix(&outputs[0], PX4IO_SERVO_COUNT, &r_mixer_limits);
-		in_mixer = false;
+		mixed = mixer_mix_threadsafe(&outputs[0], &r_mixer_limits);
 
 		/* the pwm limit call takes care of out of band errors */
 		pwm_limit_calc(should_arm, should_arm_nothrottle, mixed, r_setup_pwm_reverse, r_page_servo_disarmed,
@@ -549,7 +564,8 @@ mixer_set_failsafe()
 	}
 
 	/* mix */
-	mixed = mixer_group.mix(&outputs[0], PX4IO_SERVO_COUNT, &r_mixer_limits);
+
+	mixed = mixer_mix_threadsafe(&outputs[0], &r_mixer_limits);
 
 	/* scale to PWM and update the servo outputs as required */
 	for (unsigned i = 0; i < mixed; i++) {
diff --git a/src/modules/px4iofirmware/px4io.h b/src/modules/px4iofirmware/px4io.h
index 566c31635a..0894c9a173 100644
--- a/src/modules/px4iofirmware/px4io.h
+++ b/src/modules/px4iofirmware/px4io.h
@@ -77,7 +77,7 @@
 /*
  * Registers.
  */
-extern uint16_t			r_page_status[];	/* PX4IO_PAGE_STATUS */
+extern volatile uint16_t	r_page_status[];	/* PX4IO_PAGE_STATUS */
 extern uint16_t			r_page_actuators[];	/* PX4IO_PAGE_ACTUATORS */
 extern uint16_t			r_page_servos[];	/* PX4IO_PAGE_SERVOS */
 extern uint16_t			r_page_raw_rc_input[];	/* PX4IO_PAGE_RAW_RC_INPUT */
@@ -85,7 +85,7 @@ extern uint16_t			r_page_rc_input[];	/* PX4IO_PAGE_RC_INPUT */
 extern uint16_t			r_page_adc[];		/* PX4IO_PAGE_RAW_ADC_INPUT */
 
 extern volatile uint16_t	r_page_setup[];		/* PX4IO_PAGE_SETUP */
-extern volatile uint16_t	r_page_controls[];	/* PX4IO_PAGE_CONTROLS */
+extern uint16_t			r_page_controls[];	/* PX4IO_PAGE_CONTROLS */
 extern uint16_t			r_page_rc_input_config[]; /* PX4IO_PAGE_RC_INPUT_CONFIG */
 extern uint16_t			r_page_servo_failsafe[]; /* PX4IO_PAGE_FAILSAFE_PWM */
 extern uint16_t			r_page_servo_control_min[]; /* PX4IO_PAGE_CONTROL_MIN_PWM */
diff --git a/src/modules/px4iofirmware/registers.c b/src/modules/px4iofirmware/registers.c
index ecb7beaeaa..7be03efec3 100644
--- a/src/modules/px4iofirmware/registers.c
+++ b/src/modules/px4iofirmware/registers.c
@@ -83,7 +83,7 @@ static const uint16_t	r_page_config[] = {
  *
  * Status values.
  */
-uint16_t		r_page_status[] = {
+volatile uint16_t	r_page_status[] = {
 	[PX4IO_P_STATUS_FREEMEM]		= 0,
 	[PX4IO_P_STATUS_CPULOAD]		= 0,
 	[PX4IO_P_STATUS_FLAGS]			= 0,
@@ -214,7 +214,7 @@ volatile uint16_t	r_page_setup[] = {
  *
  * Control values from the FMU.
  */
-volatile uint16_t	r_page_controls[PX4IO_CONTROL_GROUPS * PX4IO_CONTROL_CHANNELS];
+uint16_t	r_page_controls[PX4IO_CONTROL_GROUPS * PX4IO_CONTROL_CHANNELS];
 
 /*
  * PAGE 102 does not have a buffer.