diff --git a/libraries/AP_HAL/AP_HAL_Boards.h b/libraries/AP_HAL/AP_HAL_Boards.h
index e7bd47e709..04a7133fbc 100644
--- a/libraries/AP_HAL/AP_HAL_Boards.h
+++ b/libraries/AP_HAL/AP_HAL_Boards.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_BOARDS_H__
-#define __AP_HAL_BOARDS_H__
+#pragma once
 
 /**
  * C preprocesor enumeration of the boards supported by the AP_HAL.
@@ -463,5 +461,3 @@
 #ifndef HAL_PARAM_DEFAULTS_PATH
 #define HAL_PARAM_DEFAULTS_PATH NULL
 #endif
-
-#endif // __AP_HAL_BOARDS_H__
diff --git a/libraries/AP_HAL/AP_HAL_Macros.h b/libraries/AP_HAL/AP_HAL_Macros.h
index 18b843f882..2fa8d84e6a 100644
--- a/libraries/AP_HAL/AP_HAL_Macros.h
+++ b/libraries/AP_HAL/AP_HAL_Macros.h
@@ -1,5 +1,4 @@
-#ifndef __AP_HAL_MACROS_H__
-#define __AP_HAL_MACROS_H__
+#pragma once
 
 /*
   macros to allow code to build on multiple platforms more easily
@@ -18,5 +17,3 @@
 #endif
 
 #define NORETURN __attribute__ ((noreturn))
-
-#endif // __AP_HAL_MACROS_H__
diff --git a/libraries/AP_HAL/AP_HAL_Main.h b/libraries/AP_HAL/AP_HAL_Main.h
index 9b8976fa4b..2a3954936b 100644
--- a/libraries/AP_HAL/AP_HAL_Main.h
+++ b/libraries/AP_HAL/AP_HAL_Main.h
@@ -1,5 +1,4 @@
-#ifndef __AP_HAL_MAIN_H__
-#define __AP_HAL_MAIN_H__
+#pragma once
 
 #include "HAL.h"
 
@@ -56,5 +55,3 @@
     }
 
 #endif
-
-#endif // __AP_HAL_MAIN_H__
diff --git a/libraries/AP_HAL/AP_HAL_Namespace.h b/libraries/AP_HAL/AP_HAL_Namespace.h
index 74753303ce..b5128ff012 100644
--- a/libraries/AP_HAL/AP_HAL_Namespace.h
+++ b/libraries/AP_HAL/AP_HAL_Namespace.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_NAMESPACE_H__
-#define __AP_HAL_NAMESPACE_H__
+#pragma once
 
 #include "string.h"
 #include "utility/functor.h"
@@ -70,5 +68,3 @@ namespace AP_HAL {
     // Must be implemented by the concrete HALs.
     const HAL& get_HAL();
 }
-
-#endif // __AP_HAL_NAMESPACE_H__
diff --git a/libraries/AP_HAL/AnalogIn.h b/libraries/AP_HAL/AnalogIn.h
index 279c300c3c..b69367952f 100644
--- a/libraries/AP_HAL/AnalogIn.h
+++ b/libraries/AP_HAL/AnalogIn.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_ANALOG_IN_H__
-#define __AP_HAL_ANALOG_IN_H__
+#pragma once
 
 #include <inttypes.h>
 
@@ -56,6 +54,3 @@ public:
 
 #define ANALOG_INPUT_BOARD_VCC 254
 #define ANALOG_INPUT_NONE 255
-
-#endif // __AP_HAL_ANALOG_IN_H__
-
diff --git a/libraries/AP_HAL/GPIO.h b/libraries/AP_HAL/GPIO.h
index 4158fd26dd..03ac83a5d4 100644
--- a/libraries/AP_HAL/GPIO.h
+++ b/libraries/AP_HAL/GPIO.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_GPIO_H__
-#define __AP_HAL_GPIO_H__
+#pragma once
 
 #include <stdint.h>
 
@@ -48,5 +46,3 @@ public:
     /* return true if USB cable is connected */
     virtual bool    usb_connected(void) = 0;
 };
-
-#endif // __AP_HAL_GPIO_H__
diff --git a/libraries/AP_HAL/HAL.h b/libraries/AP_HAL/HAL.h
index 8967784c68..a7e517f2b5 100644
--- a/libraries/AP_HAL/HAL.h
+++ b/libraries/AP_HAL/HAL.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_HAL_H__
-#define __AP_HAL_HAL_H__
+#pragma once
 
 #include "AP_HAL_Namespace.h"
 
@@ -97,6 +95,3 @@ public:
     AP_HAL::Util        *util;
     AP_HAL::OpticalFlow *opticalflow;
 };
-
-#endif // __AP_HAL_HAL_H__
-
diff --git a/libraries/AP_HAL/I2CDriver.h b/libraries/AP_HAL/I2CDriver.h
index 092f69467d..06898b4fe9 100644
--- a/libraries/AP_HAL/I2CDriver.h
+++ b/libraries/AP_HAL/I2CDriver.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_I2C_DRIVER_H__
-#define __AP_HAL_I2C_DRIVER_H__
+#pragma once
 
 #include <stdint.h>
 
@@ -49,6 +47,3 @@ public:
 protected:
     bool _ignore_errors;
 };
-
-#endif // __AP_HAL_I2C_DRIVER_H__
-
diff --git a/libraries/AP_HAL/RCInput.h b/libraries/AP_HAL/RCInput.h
index 9336a26a4a..e3a4dde4b4 100644
--- a/libraries/AP_HAL/RCInput.h
+++ b/libraries/AP_HAL/RCInput.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_RC_INPUT_H__
-#define __AP_HAL_RC_INPUT_H__
+#pragma once
 
 #include "AP_HAL_Namespace.h"
 
@@ -56,6 +54,3 @@ public:
     /* execute receiver bind */
     virtual bool rc_bind(int dsmMode) { return false; };
 };
-
-#endif // __AP_HAL_RC_INPUT_H__
-
diff --git a/libraries/AP_HAL/RCOutput.h b/libraries/AP_HAL/RCOutput.h
index 17c091d2f3..440380cc2c 100644
--- a/libraries/AP_HAL/RCOutput.h
+++ b/libraries/AP_HAL/RCOutput.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_RC_OUTPUT_H__
-#define __AP_HAL_RC_OUTPUT_H__
+#pragma once
 
 #include "AP_HAL_Namespace.h"
 
@@ -104,6 +102,3 @@ public:
      */
     virtual void     set_esc_scaling(uint16_t min_pwm, uint16_t max_pwm) {}
 };
-
-#endif // __AP_HAL_RC_OUTPUT_H__
-
diff --git a/libraries/AP_HAL/Scheduler.h b/libraries/AP_HAL/Scheduler.h
index 0ca81e889d..6c84db550a 100644
--- a/libraries/AP_HAL/Scheduler.h
+++ b/libraries/AP_HAL/Scheduler.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_SCHEDULER_H__
-#define __AP_HAL_SCHEDULER_H__
+#pragma once
 
 #include <stdint.h>
 
@@ -63,6 +61,3 @@ public:
      */
     virtual void     stop_clock(uint64_t time_usec) {}
 };
-
-#endif // __AP_HAL_SCHEDULER_H__
-
diff --git a/libraries/AP_HAL/Semaphores.h b/libraries/AP_HAL/Semaphores.h
index 6dfa3d0c13..4c1ee68984 100644
--- a/libraries/AP_HAL/Semaphores.h
+++ b/libraries/AP_HAL/Semaphores.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_SEMAPHORES_H__
-#define __AP_HAL_SEMAPHORES_H__
+#pragma once
 
 #include "AP_HAL_Namespace.h"
 
@@ -12,5 +10,3 @@ public:
     virtual bool take_nonblocking() WARN_IF_UNUSED = 0;
     virtual bool give() = 0;
 };
-
-#endif  // __AP_HAL_SEMAPHORES_H__
diff --git a/libraries/AP_HAL/Storage.h b/libraries/AP_HAL/Storage.h
index 4a1b4b5338..15c3617a46 100644
--- a/libraries/AP_HAL/Storage.h
+++ b/libraries/AP_HAL/Storage.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_STORAGE_H__
-#define __AP_HAL_STORAGE_H__
+#pragma once
 
 #include <stdint.h>
 #include "AP_HAL_Namespace.h"
@@ -11,6 +9,3 @@ public:
     virtual void read_block(void *dst, uint16_t src, size_t n) = 0;
     virtual void write_block(uint16_t dst, const void* src, size_t n) = 0;
 };
-
-#endif // __AP_HAL_STORAGE_H__
-
diff --git a/libraries/AP_HAL/UARTDriver.h b/libraries/AP_HAL/UARTDriver.h
index edee85bd96..3564038f7b 100644
--- a/libraries/AP_HAL/UARTDriver.h
+++ b/libraries/AP_HAL/UARTDriver.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_UART_DRIVER_H__
-#define __AP_HAL_UART_DRIVER_H__
+#pragma once
 
 #include <stdint.h>
 
@@ -54,6 +52,3 @@ public:
     void printf(const char *s, ...) FMT_PRINTF(2, 3);
     void vprintf(const char *s, va_list ap);
 };
-
-#endif // __AP_HAL_UART_DRIVER_H__
-
diff --git a/libraries/AP_HAL/Util.h b/libraries/AP_HAL/Util.h
index 30c35a6d54..e232746480 100644
--- a/libraries/AP_HAL/Util.h
+++ b/libraries/AP_HAL/Util.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_UTIL_H__
-#define __AP_HAL_UTIL_H__
+#pragma once
 
 #include <stdarg.h>
 #include "AP_HAL_Namespace.h"
@@ -104,6 +102,3 @@ protected:
     bool soft_armed = false;
     uint64_t capabilities = 0;
 };
-
-#endif // __AP_HAL_UTIL_H__
-
diff --git a/libraries/AP_HAL/utility/BetterStream.h b/libraries/AP_HAL/utility/BetterStream.h
index 5bef6a75f4..bdd6e2c83d 100644
--- a/libraries/AP_HAL/utility/BetterStream.h
+++ b/libraries/AP_HAL/utility/BetterStream.h
@@ -17,9 +17,7 @@
 //      Copyright (c) 2010 Michael Smith. All rights reserved.
 //
 //
-
-#ifndef __AP_HAL_UTILITY_BETTERSTREAM_H__
-#define __AP_HAL_UTILITY_BETTERSTREAM_H__
+#pragma once
 
 #include <stdarg.h>
 
@@ -35,6 +33,3 @@ public:
     virtual void printf(const char *, ...) FMT_PRINTF(2, 3) = 0;
     virtual void vprintf(const char *, va_list) = 0;
 };
-
-#endif // __AP_HAL_UTILITY_BETTERSTREAM_H__
-
diff --git a/libraries/AP_HAL/utility/Print.h b/libraries/AP_HAL/utility/Print.h
index 8b98dbe95a..32dd99ddac 100644
--- a/libraries/AP_HAL/utility/Print.h
+++ b/libraries/AP_HAL/utility/Print.h
@@ -16,9 +16,7 @@
   License along with this library; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
-
-#ifndef __AP_HAL_UTILITY_PRINT_H__
-#define __AP_HAL_UTILITY_PRINT_H__
+#pragma once
 
 #include <AP_HAL/AP_HAL_Namespace.h>
 
@@ -75,6 +73,3 @@ class AP_HAL::Print {
     size_t println(void);
 
 };
-
-#endif // __AP_HAL_UTILITY_PRINT_H__
-
diff --git a/libraries/AP_HAL/utility/Socket.h b/libraries/AP_HAL/utility/Socket.h
index adc298605b..17a14817ef 100644
--- a/libraries/AP_HAL/utility/Socket.h
+++ b/libraries/AP_HAL/utility/Socket.h
@@ -15,9 +15,7 @@
 /*
   simple socket handling class for systems with BSD socket API
  */
-
-#ifndef HAL_SOCKET_H
-#define HAL_SOCKET_H
+#pragma once
 
 #include <AP_HAL/AP_HAL.h>
 #if HAL_OS_SOCKETS
@@ -73,4 +71,3 @@ private:
 };
 
 #endif // HAL_OS_SOCKETS
-#endif // HAL_SOCKET_H
diff --git a/libraries/AP_HAL/utility/Stream.h b/libraries/AP_HAL/utility/Stream.h
index e382a86f86..749dddfe30 100644
--- a/libraries/AP_HAL/utility/Stream.h
+++ b/libraries/AP_HAL/utility/Stream.h
@@ -1,6 +1,4 @@
-
-#ifndef __AP_HAL_UTILITY_STREAM_H__
-#define __AP_HAL_UTILITY_STREAM_H__
+#pragma once
 
 #include <AP_HAL/AP_HAL_Namespace.h>
 #include "Print.h"
@@ -20,6 +18,3 @@ public:
     virtual int16_t read() = 0;
 
 };
-
-#endif // __AP_HAL_UTILITY_STREAM_H__
-
diff --git a/libraries/AP_HAL/utility/ftoa_engine.h b/libraries/AP_HAL/utility/ftoa_engine.h
index ba3c042b33..7566d5d3c8 100644
--- a/libraries/AP_HAL/utility/ftoa_engine.h
+++ b/libraries/AP_HAL/utility/ftoa_engine.h
@@ -27,9 +27,7 @@
   POSSIBILITY OF SUCH DAMAGE. */
 
 /* $Id: ftoa_engine.h 1218 2007-02-18 13:18:41Z dmix $ */
-
-#ifndef	_FTOA_ENGINE_H
-#define	_FTOA_ENGINE_H
+#pragma once
 
 #include <AP_HAL/AP_HAL.h>
 #include <stdint.h>
@@ -43,5 +41,3 @@ int16_t ftoa_engine(float val, char *buf,
 #define	FTOA_INF	4
 #define	FTOA_NAN	8
 #define	FTOA_CARRY	16	/* Carry was to master position.	*/
-
-#endif	/* !_FTOA_ENGINE_H */
diff --git a/libraries/AP_HAL/utility/getopt_cpp.h b/libraries/AP_HAL/utility/getopt_cpp.h
index c1ccef0273..eb10c039a2 100644
--- a/libraries/AP_HAL/utility/getopt_cpp.h
+++ b/libraries/AP_HAL/utility/getopt_cpp.h
@@ -8,8 +8,7 @@
  * Simple conversion to C++ by Andrew Tridgell for ArduPilot. Based on
  * getopt_long.h from ccache
  */
-#ifndef GETOPT_LONG_H
-#define GETOPT_LONG_H
+#pragma once
 
 #include <stdbool.h>
 
@@ -45,5 +44,3 @@ private:
     const struct option *longopts;
     const char *place;
 };
-
-#endif  /* GETOPT_LONG_H */
diff --git a/libraries/AP_HAL/utility/xtoa_fast.h b/libraries/AP_HAL/utility/xtoa_fast.h
index 21462c7b2a..b3ebeded77 100644
--- a/libraries/AP_HAL/utility/xtoa_fast.h
+++ b/libraries/AP_HAL/utility/xtoa_fast.h
@@ -30,9 +30,7 @@
   POSSIBILITY OF SUCH DAMAGE. */
 
 /* $Id: xtoa_fast.h 1223 2007-02-18 13:33:09Z dmix $	*/
-
-#ifndef	_XTOA_FAST_H_
-#define _XTOA_FAST_H_
+#pragma once
 
 /* Internal function for use from `printf'.	*/
 char *ultoa_invert (uint32_t val, char *s, uint8_t base);
@@ -41,5 +39,3 @@ char *ulltoa_invert (uint64_t val, char *s, uint8_t base);
 /* Next flags are to use with `base'. Unused fields are reserved.	*/
 #define XTOA_PREFIX	0x0100	/* put prefix for octal or hex	*/
 #define XTOA_UPPER	0x0200	/* use upper case letters	*/
-
-#endif	/* _XTOA_FAST_H_ */