Index: head/usr.sbin/pwd_mkdb/Makefile
===================================================================
--- head/usr.sbin/pwd_mkdb/Makefile
+++ head/usr.sbin/pwd_mkdb/Makefile
@@ -9,5 +9,8 @@
 SRCS=	pw_scan.c pwd_mkdb.c
 
 CFLAGS+= -I${SRCTOP}/lib/libc/gen		# for pw_scan.h
+.if defined(BOOTSTRAPPING)
+CFLAGS+=-I${.CURDIR}
+.endif
 
 .include <bsd.prog.mk>
Index: head/usr.sbin/pwd_mkdb/pwd.h
===================================================================
--- head/usr.sbin/pwd_mkdb/pwd.h
+++ head/usr.sbin/pwd_mkdb/pwd.h
@@ -0,0 +1,66 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2018-2020 Alex Richardson <arichardson@FreeBSD.org>
+ *
+ * This software was developed by SRI International and the University of
+ * Cambridge Computer Laboratory (Department of Computer Science and
+ * Technology) under DARPA contract HR0011-18-C-0016 ("ECATS"), as part of the
+ * DARPA SSITH research programme.
+ *
+ * This software was developed by SRI International and the University of
+ * Cambridge Computer Laboratory under DARPA/AFRL contract (FA8750-10-C-0237)
+ * ("CTSRD"), as part of the DARPA CRASH research programme.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+/*
+ * When building pwd_mkdb we need to use target systems definition of
+ * struct passwd. This protects against future changes to struct passwd and
+ * is essential to allow cross-building from Linux/macOS hosts since the
+ * structure is not compatible there.
+ */
+#include <stdint.h>
+#include <stddef.h>
+/*
+ * Note: pwd_mkdb always stores uint32_t for all integer fields (including
+ * time_t!) so these definitions do not need to match sys/sys/_types.h
+ */
+typedef	uint32_t	_bootstrap_gid_t;
+typedef	uint32_t	_bootstrap_uid_t;
+typedef	uint64_t	_bootstrap_time_t;
+#define	_GID_T_DECLARED
+#define	_TIME_T_DECLARED
+#define	_UID_T_DECLARED
+#define	_SIZE_T_DECLARED
+
+#define	gid_t	_bootstrap_gid_t
+#define	uid_t	_bootstrap_uid_t
+#define	time_t	_bootstrap_time_t
+#define	passwd	_bootstrap_passwd
+#include "../../include/pwd.h"
+#undef gid_t
+#undef uid_t
+#undef time_t