diff --git a/cddl/lib/libdtrace/Makefile b/cddl/lib/libdtrace/Makefile
--- a/cddl/lib/libdtrace/Makefile
+++ b/cddl/lib/libdtrace/Makefile
@@ -131,6 +131,10 @@
 DSRCS+=		regs_riscv.d
 .endif
 
+.if ${MACHINE_CPUARCH} == "aarch64"
+SRCS+=		instr_size.c
+.endif
+
 YFLAGS+=-d
 
 LIBADD=	ctf elf proc pthread rtld_db
diff --git a/sys/cddl/dev/dtrace/aarch64/instr_size.c b/sys/cddl/dev/dtrace/aarch64/instr_size.c
new file mode 100644
--- /dev/null
+++ b/sys/cddl/dev/dtrace/aarch64/instr_size.c
@@ -0,0 +1,14 @@
+/*
+ * SPDX-License-Identifier: CDDL 1.0
+ *
+ * Copyright 2023 Christos Margiolis <christos@FreeBSD.org>
+ */
+
+#include <sys/types.h>
+#include <sys/dtrace.h>
+
+int
+dtrace_instr_size(uint8_t *instr __unused)
+{
+	return (INSN_SIZE);
+}
diff --git a/sys/modules/dtrace/dtrace/Makefile b/sys/modules/dtrace/dtrace/Makefile
--- a/sys/modules/dtrace/dtrace/Makefile
+++ b/sys/modules/dtrace/dtrace/Makefile
@@ -24,7 +24,7 @@
                -I${SYSDIR}/cddl/dev/dtrace/x86
 .endif
 
-.if ${MACHINE_CPUARCH} == "riscv"
+.if ${MACHINE_CPUARCH} == "riscv" || ${MACHINE_CPUARCH} == "aarch64"
 SRCS+=		instr_size.c
 .endif