diff --git a/src/avr/adc.c b/src/avr/adc.c
index 99fd063f6..e94dfbc57 100644
--- a/src/avr/adc.c
+++ b/src/avr/adc.c
@@ -4,6 +4,7 @@
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
+#include <avr/io.h> // ADCSRA
 #include "autoconf.h" // CONFIG_MACH_atmega644p
 #include "command.h" // shutdown
 #include "gpio.h" // gpio_adc_read
diff --git a/src/avr/main.c b/src/avr/main.c
index 0523af411..b0d299dac 100644
--- a/src/avr/main.c
+++ b/src/avr/main.c
@@ -12,6 +12,12 @@
 #include "irq.h" // irq_enable
 #include "sched.h" // sched_main
 
+// Newer avr-libc headers expose the stack pointer as SP instead of the
+// older AVR_STACK_POINTER_REG alias used by Klipper.
+#ifndef AVR_STACK_POINTER_REG
+#define AVR_STACK_POINTER_REG SP
+#endif
+
 DECL_CONSTANT_STR("MCU", CONFIG_MCU);
 
 
diff --git a/src/avr/spi.c b/src/avr/spi.c
index 55eb1f58c..d8acd45da 100644
--- a/src/avr/spi.c
+++ b/src/avr/spi.c
@@ -4,6 +4,7 @@
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
+#include <avr/io.h> // SPCR
 #include "autoconf.h" // CONFIG_MACH_atmega644p
 #include "command.h" // shutdown
 #include "gpio.h" // spi_setup