diff --git a/src/avclan/avclan_defs.h b/src/avclan/avclan_defs.h
index b632f0c..029993a 100644
--- a/src/avclan/avclan_defs.h
+++ b/src/avclan/avclan_defs.h
@@ -7,8 +7,7 @@
 // (phy / frame / protocol / cdchanger). This is a leaf header: it must not
 // include any other project header.
 
-#ifndef AVCLAN_DEFS_H
-#define AVCLAN_DEFS_H
+#pragma once
 
 #include <stdint.h>
 
@@ -157,5 +156,3 @@ typedef enum : uint8_t {
   sBUSY,
   sMUTED,
 } avclan_senderr_t;
-
-#endif // AVCLAN_DEFS_H
diff --git a/src/avclan/avclan_frame.h b/src/avclan/avclan_frame.h
index b67b1fd..708ce08 100644
--- a/src/avclan/avclan_frame.h
+++ b/src/avclan/avclan_frame.h
@@ -29,17 +29,22 @@
   No acknowledge bits are sent for broadcast frames.
 */
 
-#ifndef AVCLAN_FRAME_H
-#define AVCLAN_FRAME_H
+#pragma once
 
 #include <stdint.h>
 
 #include "avclan_defs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 avclan_readerr_t AVCLAN_readframe(AVCLAN_frame_t *frame, log_t print);
 avclan_senderr_t AVCLAN_sendframe(const AVCLAN_frame_t *frame, log_t print);
 void AVCLAN_printframe(const AVCLAN_frame_t *frame, bool binary);
 uint8_t AVCLAN_parseframe(const uint8_t *bytes, uint8_t len,
                           AVCLAN_frame_t *frame);
 
-#endif // AVCLAN_FRAME_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/avclan_phy.h b/src/avclan/avclan_phy.h
index 7c061c2..7864b9c 100644
--- a/src/avclan/avclan_phy.h
+++ b/src/avclan/avclan_phy.h
@@ -3,13 +3,16 @@
 // Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-#ifndef AVCLAN_PHY_H
-#define AVCLAN_PHY_H
+#pragma once
 
 #include <stdint.h>
 
 #include "avclan_defs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 // One-time bring-up of the bus hardware. Leaves the bus idle and TX unmuted.
 void AVCLAN_busInit(void);
 
@@ -69,4 +72,6 @@ uint8_t AVCLAN_readbyte(uint8_t *byte);
 void AVCLan_Measure(void);
 #endif
 
-#endif // AVCLAN_PHY_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/avclan_protocol.h b/src/avclan/avclan_protocol.h
index 2e1b9c1..f8fc066 100644
--- a/src/avclan/avclan_protocol.h
+++ b/src/avclan/avclan_protocol.h
@@ -5,13 +5,16 @@
 // generic peripheral-level handling with CD-changer device-specific handling;
 // the device-specific cases will later migrate into cdchanger.
 
-#ifndef AVCLAN_PROTOCOL_H
-#define AVCLAN_PROTOCOL_H
+#pragma once
 
 #include <stdint.h>
 
 #include "avclan_defs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /// Message state machine
 // - r_Nothing (0x00) means don't send current message
 // - r_Handled means send current message and stop/finished state machine
@@ -37,4 +40,6 @@ typedef struct RFrame_struct {
 response_t AVCLAN_handleframe(const AVCLAN_frame_t *in, AVCLAN_frame_t *out);
 RFrame_t *AVCLAN_statemachine(RFrame_t *resp);
 
-#endif // AVCLAN_PROTOCOL_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/avclandrv.h b/src/avclan/avclandrv.h
index 8ab8491..dc4c137 100644
--- a/src/avclan/avclandrv.h
+++ b/src/avclan/avclandrv.h
@@ -6,8 +6,7 @@
 // Umbrella header for the avclan library. Consumers (e.g. the app in
 // src/sniffer.c) include this single header to pull in the whole AVC-LAN stack.
 
-#ifndef __AVCLANDRV_H
-#define __AVCLANDRV_H
+#pragma once
 
 #include "avclan_defs.h"
 #include "avclan_frame.h"
@@ -16,5 +15,3 @@
 #include "cdchanger.h"
 #include "mediacontrol.h"
 #include "statustimer.h"
-
-#endif // __AVCLANDRV_H
diff --git a/src/avclan/cdchanger.h b/src/avclan/cdchanger.h
index 5e42b37..ee722d6 100644
--- a/src/avclan/cdchanger.h
+++ b/src/avclan/cdchanger.h
@@ -8,13 +8,16 @@
 // logic; it commands the mediacontrol and statustimer drivers rather than
 // touching their hardware directly.
 
-#ifndef CDCHANGER_H
-#define CDCHANGER_H
+#pragma once
 
 #include <stdint.h>
 
 #include "avclan_defs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef enum : uint8_t {
   cd_OPEN = 0x01,
   cd_ERR1 = 0x02,
@@ -77,4 +80,6 @@ void serializeCDStatus(uint8_t *dst);
 AVCLAN_frame_t *AVCLAN_getStatusFrame();
 void AVCLAN_generateStatus(AVCLAN_frame_t *status, bool is_unicast, devices to);
 
-#endif // CDCHANGER_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/mediacontrol.h b/src/avclan/mediacontrol.h
index 7e813f8..9d2d44d 100644
--- a/src/avclan/mediacontrol.h
+++ b/src/avclan/mediacontrol.h
@@ -3,8 +3,7 @@
 
 // Media-control: route/handle head-unit button presses to the audio source.
 
-#ifndef MEDIACONTROL_H
-#define MEDIACONTROL_H
+#pragma once
 
 #include <stdint.h>
 
@@ -15,6 +14,10 @@ typedef enum : uint8_t {
   MEDIA_SKIP_BACKWARD,
 } AVCLAN_media_fn_t;
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 // One-time hardware bring-up for the media driver.
 void mediacontrol_init();
 
@@ -26,4 +29,6 @@ bool AVCLAN_micToggle();
 bool AVCLAN_isMediaFunctioning();
 #endif
 
-#endif // MEDIACONTROL_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/statustimer.h b/src/avclan/statustimer.h
index d0a2de6..ec615d3 100644
--- a/src/avclan/statustimer.h
+++ b/src/avclan/statustimer.h
@@ -5,8 +5,11 @@
 // polls statustimer_tickPending() and clears the tick with
 // statustimer_clearTick()
 
-#ifndef STATUSTIMER_H
-#define STATUSTIMER_H
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 // One-time hardware bring-up. Leaves the tick disabled.
 void statustimer_init(void);
@@ -23,4 +26,6 @@ extern volatile bool tick_pending;
 static inline bool statustimer_tickPending() { return tick_pending; }
 static inline void statustimer_clearTick() { tick_pending = false; }
 
-#endif // STATUSTIMER_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/target/avr-attiny3216/media_avr.h b/src/avclan/target/avr-attiny3216/media_avr.h
index 64a7046..14cdebd 100644
--- a/src/avclan/target/avr-attiny3216/media_avr.h
+++ b/src/avclan/target/avr-attiny3216/media_avr.h
@@ -5,8 +5,11 @@
 // transaction guard (phy_avr.c's AVCLAN_stopEvent). Not part of the public
 // mediacontrol.h interface.
 
-#ifndef MEDIA_AVR_H
-#define MEDIA_AVR_H
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 // Keep the TCA0 press waveform roughly in sync while a bus transaction has
 // masked interrupts (runs the OVF ISR body early if an overflow is imminent).
@@ -14,4 +17,6 @@
 // ATOMIC_BLOCK).
 void mediacontrol_syncDuringMask();
 
-#endif // MEDIA_AVR_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/avclan/target/avr-attiny3216/timing_avr.h b/src/avclan/target/avr-attiny3216/timing_avr.h
index 0a6a770..37424cb 100644
--- a/src/avclan/target/avr-attiny3216/timing_avr.h
+++ b/src/avclan/target/avr-attiny3216/timing_avr.h
@@ -1,8 +1,7 @@
 // Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-#ifndef TIMING_AVR_H
-#define TIMING_AVR_H
+#pragma once
 
 // AVR ATtiny3216 timing parameters. Derives F_CPU (needed by avr-libc, e.g.
 // util/delay.h) and the bus-timer (TCB) tick period from the CMake-provided
@@ -65,5 +64,3 @@
 #define TICK_US (TCB_TICK / 1000.0)
 
 #include "timing.h"
-
-#endif // TIMING_AVR_H
diff --git a/src/avclan/timing.h b/src/avclan/timing.h
index 88df522..111137a 100644
--- a/src/avclan/timing.h
+++ b/src/avclan/timing.h
@@ -1,8 +1,7 @@
 // Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-#ifndef _TIMING_HPP_
-#define _TIMING_HPP_
+#pragma once
 
 // Physical AVC-LAN bit-phase durations, in microseconds. These are protocol
 // facts (the bus spec), independent of any particular hardware. The active
@@ -31,5 +30,3 @@
 #define AVCLAN_READBIT_THRESHOLD (26.0 / TICK_US)
 
 #define AVCLAN_BIT_LENGTH_MAX (39.1 / TICK_US)
-
-#endif
diff --git a/src/board.h b/src/board.h
index c9d8cda..1ae956e 100644
--- a/src/board.h
+++ b/src/board.h
@@ -1,8 +1,11 @@
 // Copyright (C) 2026 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-#ifndef BOARD_H
-#define BOARD_H
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 // Clock setup + GPIO/pin configuration. Call once, first thing at startup
 // (before any peripheral init).
@@ -11,4 +14,6 @@ void board_init(void);
 // Globally enable interrupts. Call after all peripherals are initialized.
 void board_interruptsEnable(void);
 
-#endif // BOARD_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/com232.h b/src/com232.h
index f90068d..ee1b3b6 100644
--- a/src/com232.h
+++ b/src/com232.h
@@ -3,11 +3,14 @@
 // Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-#ifndef __COM232_H
-#define __COM232_H
+#pragma once
 
 #include <stdint.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 void RS232_Init(void);
 
 // Receive path. The RX ring is private to the driver; the app polls hasChar()
@@ -28,4 +31,6 @@ void RS232_PrintHex(uint16_t x);
 void RS232_PrintDec(uint8_t Data);
 void RS232_PrintDec2(uint8_t Data);
 
-#endif // __COM232_H
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/queue.h b/src/queue.h
index a24c3ae..afe04c3 100644
--- a/src/queue.h
+++ b/src/queue.h
@@ -5,6 +5,10 @@
 
 #include <stdint.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef struct Queue_struct {
   uint8_t write;
   uint8_t read;
@@ -20,3 +24,7 @@ static inline void incrementRead(Queue_t *q) { q->read++; }
 uint8_t pushQueue(Queue_t *q, void *x);
 void *peekQueue(const Queue_t *q);
 void *popQueue(Queue_t *q);
+
+#ifdef __cplusplus
+}
+#endif