diff --git a/sys/arm/include/pcpu.h b/sys/arm/include/pcpu.h
index edf7f37d191..89f1e1df4e2 100644
--- a/sys/arm/include/pcpu.h
+++ b/sys/arm/include/pcpu.h
@@ -37,8 +37,6 @@
 #include <sys/_lock.h>
 #include <sys/_mutex.h>
 
-#define	ALT_STACK_SIZE	128
-
 struct vmspace;
 
 #endif	/* _KERNEL */
diff --git a/sys/arm64/include/pcpu.h b/sys/arm64/include/pcpu.h
index ebb72799d83..de0383c4cd8 100644
--- a/sys/arm64/include/pcpu.h
+++ b/sys/arm64/include/pcpu.h
@@ -37,8 +37,6 @@
 #include <machine/cpu.h>
 #include <machine/cpufunc.h>
 
-#define	ALT_STACK_SIZE	128
-
 typedef int (*pcpu_bp_harden)(void);
 typedef int (*pcpu_ssbd)(int);
 struct debug_monitor_state;
diff --git a/sys/riscv/include/pcpu.h b/sys/riscv/include/pcpu.h
index 0165a271250..20d948931f4 100644
--- a/sys/riscv/include/pcpu.h
+++ b/sys/riscv/include/pcpu.h
@@ -42,8 +42,6 @@
 #include <machine/cpu.h>
 #include <machine/cpufunc.h>
 
-#define	ALT_STACK_SIZE	128
-
 /* Keep in sync with db_show_mdpcpu() */
 #define	PCPU_MD_FIELDS							\
 	struct pmap *pc_curpmap;	/* Currently active pmap */	\