diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c
--- a/sys/kern/kern_ktrace.c
+++ b/sys/kern/kern_ktrace.c
@@ -142,6 +142,7 @@
 	struct ktr_header kth;
 	struct ktr_sysret ktp;
 
+	bzero(&ktp, sizeof(ktp));
 	lp->lwp_traceflag |= KTRFAC_ACTIVE;
 	ktrgetheader(&kth, KTR_SYSRET);