diff --git a/sys/amd64/linux/linux_machdep.c b/sys/amd64/linux/linux_machdep.c
--- a/sys/amd64/linux/linux_machdep.c
+++ b/sys/amd64/linux/linux_machdep.c
@@ -350,12 +350,6 @@
 		linux_msg(td, "PT_LWPINFO failed with error %d", error);
 		return (error);
 	}
-	if ((lwpinfo.pl_flags & PL_FLAG_SCE) != 0) {
-		/*
-		 * Undo the mangling done in exception.S:fast_syscall_common().
-		 */
-		l_regset->r10 = l_regset->rcx;
-	}
 	if ((lwpinfo.pl_flags & (PL_FLAG_SCE | PL_FLAG_SCX)) != 0) {
 		/*
 		 * In Linux, the syscall number - passed to the syscall
diff --git a/sys/amd64/linux/linux_sysvec.c b/sys/amd64/linux/linux_sysvec.c
--- a/sys/amd64/linux/linux_sysvec.c
+++ b/sys/amd64/linux/linux_sysvec.c
@@ -167,6 +167,9 @@
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
+	/* Restore r10 earlier to avoid doing this multiply times. */
+	frame->tf_r10 = frame->tf_rcx;
+
 	td->td_retval[0] = 0;
 	return (0);
 }
@@ -181,7 +184,6 @@
 	switch (error) {
 	case 0:
 		frame->tf_rax = td->td_retval[0];
-		frame->tf_r10 = frame->tf_rcx;
 		break;
 
 	case ERESTART:
@@ -192,7 +194,6 @@
 		 *
 		 */
 		frame->tf_rip -= frame->tf_err;
-		frame->tf_r10 = frame->tf_rcx;
 		break;
 
 	case EJUSTRETURN:
@@ -200,7 +201,6 @@
 
 	default:
 		frame->tf_rax = bsd_to_linux_errno(error);
-		frame->tf_r10 = frame->tf_rcx;
 		break;
 	}