diff --git a/src/modules/systemlib/perf_counter.c b/src/modules/systemlib/perf_counter.c
index 227119df7d..07f51eacc4 100644
--- a/src/modules/systemlib/perf_counter.c
+++ b/src/modules/systemlib/perf_counter.c
@@ -294,7 +294,7 @@ perf_end(perf_counter_t handle)
 	}
 }
 
-#include <systemlib/err.h>
+#include "systemlib/err.h"
 
 void
 perf_set_elapsed(perf_counter_t handle, int64_t elapsed)
diff --git a/src/modules/systemlib/perf_counter.h b/src/modules/systemlib/perf_counter.h
index f4669f172f..ced816e76a 100644
--- a/src/modules/systemlib/perf_counter.h
+++ b/src/modules/systemlib/perf_counter.h
@@ -64,7 +64,9 @@ __BEGIN_DECLS
  * @return			Handle for the new counter, or NULL if a counter
  *				could not be allocated.
  */
+#ifndef perf_alloc	// perf_alloc might be defined to be NULL in src/modules/px4iofirmware/px4io.h
 __EXPORT extern perf_counter_t	perf_alloc(enum perf_counter_type type, const char *name);
+#endif
 
 /**
  * Get the reference to an existing counter or create a new one if it does not exist.
diff --git a/src/platforms/posix/include/queue.h b/src/platforms/posix/include/queue.h
index 30dc264f3f..d6315ca172 100644
--- a/src/platforms/posix/include/queue.h
+++ b/src/platforms/posix/include/queue.h
@@ -42,6 +42,12 @@
 
 #include <sys/types.h>
 
+#ifdef __cplusplus
+#include <cstddef>	// NULL
+#else
+#include <stddef.h>	// NULL
+#endif
+
 /************************************************************************
  * Pre-processor Definitions
  ************************************************************************/
@@ -61,9 +67,6 @@
 
 // Required for Linux
 #define FAR
-#ifndef NULL
-#define NULL (void *)0
-#endif
 
 /************************************************************************
  * Global Type Declarations
diff --git a/src/platforms/posix/px4_layer/drv_hrt.c b/src/platforms/posix/px4_layer/drv_hrt.c
index 8f7b99592d..4f9b4e824c 100644
--- a/src/platforms/posix/px4_layer/drv_hrt.c
+++ b/src/platforms/posix/px4_layer/drv_hrt.c
@@ -94,7 +94,6 @@ static void hrt_unlock(void)
 }
 
 #if defined(__PX4_APPLE_LEGACY)
-#include <time.h>
 #include <sys/time.h>
 
 int px4_clock_gettime(clockid_t clk_id, struct timespec *tp)
diff --git a/src/platforms/posix/work_queue/hrt_work_cancel.c b/src/platforms/posix/work_queue/hrt_work_cancel.c
index d8c5957c0b..a1af842ca5 100644
--- a/src/platforms/posix/work_queue/hrt_work_cancel.c
+++ b/src/platforms/posix/work_queue/hrt_work_cancel.c
@@ -39,8 +39,8 @@
 
 #include <px4_config.h>
 #include <px4_defines.h>
-#include <queue.h>
 #include <px4_workqueue.h>
+
 #include "hrt_work.h"
 
 /****************************************************************************
diff --git a/src/platforms/qurt/include/queue.h b/src/platforms/qurt/include/queue.h
index 30dc264f3f..d6315ca172 100644
--- a/src/platforms/qurt/include/queue.h
+++ b/src/platforms/qurt/include/queue.h
@@ -42,6 +42,12 @@
 
 #include <sys/types.h>
 
+#ifdef __cplusplus
+#include <cstddef>	// NULL
+#else
+#include <stddef.h>	// NULL
+#endif
+
 /************************************************************************
  * Pre-processor Definitions
  ************************************************************************/
@@ -61,9 +67,6 @@
 
 // Required for Linux
 #define FAR
-#ifndef NULL
-#define NULL (void *)0
-#endif
 
 /************************************************************************
  * Global Type Declarations
diff --git a/src/platforms/qurt/px4_layer/drv_hrt.c b/src/platforms/qurt/px4_layer/drv_hrt.c
index bdc49da74a..3ca4cbfe9c 100644
--- a/src/platforms/qurt/px4_layer/drv_hrt.c
+++ b/src/platforms/qurt/px4_layer/drv_hrt.c
@@ -42,6 +42,7 @@
 #include <drivers/drv_hrt.h>
 #include <semaphore.h>
 #include <time.h>
+#include <sys/time.h>
 #include <dspal_time.h>
 #include <string.h>
 #include <stdio.h>
@@ -63,8 +64,6 @@ static void		hrt_call_reschedule(void);
 static sem_t 	_hrt_lock;
 static struct work_s	_hrt_work;
 
-#include <time.h>
-#include <sys/time.h>
 #define CLOCK_REALTIME 0
 
 #ifndef CLOCK_MONOTONIC