Index: sys/riscv/riscv/trap.c
===================================================================
--- sys/riscv/riscv/trap.c
+++ sys/riscv/riscv/trap.c
@@ -46,6 +46,7 @@
 #include <sys/ptrace.h>
 #include <sys/syscall.h>
 #include <sys/sysent.h>
+#include <sys/sysproto.h>
 #ifdef KDB
 #include <sys/kdb.h>
 #endif
@@ -106,12 +107,6 @@
 
 	sa->code = td->td_frame->tf_t[0];
 
-	if (__predict_false(sa->code == SYS_syscall || sa->code == SYS___syscall)) {
-		sa->code = *ap++;
-	} else {
-		*dst_ap++ = *ap++;
-	}
-
 	if (__predict_false(sa->code >= p->p_sysent->sv_size))
 		sa->callp = &p->p_sysent->sv_table[0];
 	else
@@ -120,7 +115,13 @@
 	KASSERT(sa->callp->sy_narg <= nitems(sa->args),
 	    ("Syscall %d takes too many arguments", sa->code));
 
-	memcpy(dst_ap, ap, (NARGREG - 1) * sizeof(register_t));
+	if (__predict_false(sa->callp->sy_call == (sy_call_t *)nosys) &&
+	    (sa->code == SYS_syscall || sa->code == SYS___syscall)) {
+		sa->code = *ap++;
+		memcpy(dst_ap, ap, (NARGREG - 1) * sizeof(register_t));
+	} else {
+		memcpy(dst_ap, ap, NARGREG * sizeof(register_t));
+	}
 
 	td->td_retval[0] = 0;
 	td->td_retval[1] = 0;