diff --git a/sys/arm64/arm64/vm_machdep.c b/sys/arm64/arm64/vm_machdep.c
--- a/sys/arm64/arm64/vm_machdep.c
+++ b/sys/arm64/arm64/vm_machdep.c
@@ -91,6 +91,9 @@
 	td2->td_pcb = pcb2;
 	bcopy(td1->td_pcb, pcb2, sizeof(*pcb2));
 
+	/* Clear the debug register state. */
+	bzero(&pcb2->pcb_dbg_regs, sizeof(pcb2->pcb_dbg_regs));
+
 	tf = (struct trapframe *)STACKALIGN((struct trapframe *)pcb2 - 1);
 	bcopy(td1->td_frame, tf, sizeof(*tf));
 	tf->tf_x[0] = 0;