Index: sys/netinet/dccp.h
===================================================================
--- sys/netinet/dccp.h
+++ sys/netinet/dccp.h
@@ -64,7 +64,7 @@
                        uint8_t seq[6];
                } longseq;
        } d_seqno;
-};
+}  __packed;
 
 #define d_seqno_short d_seqno.shortseq;
 #define d_seqno_long d_seqno.longseq.seq;
Index: sys/netinet/ip.h
===================================================================
--- sys/netinet/ip.h
+++ sys/netinet/ip.h
@@ -67,7 +67,7 @@
 	u_char	ip_p;			/* protocol */
 	u_short	ip_sum;			/* checksum */
 	struct	in_addr ip_src,ip_dst;	/* source and dest address */
-} __packed __aligned(2);
+} __packed;
 
 #define	IP_MAXPACKET	65535		/* maximum packet size */
 
@@ -187,7 +187,7 @@
 			uint32_t ipt_time;	/* network format */
 		} ipt_ta[1];
 	} ipt_timestamp;
-};
+} __packed;
 
 /* Flag bits for ipt_flg. */
 #define	IPOPT_TS_TSONLY		0		/* timestamps only */
Index: sys/netinet/ip_var.h
===================================================================
--- sys/netinet/ip_var.h
+++ sys/netinet/ip_var.h
@@ -47,7 +47,7 @@
 	u_short	ih_len;			/* protocol length */
 	struct	in_addr ih_src;		/* source internet address */
 	struct	in_addr ih_dst;		/* destination internet address */
-};
+} __packed;
 
 #ifdef _KERNEL
 /*
Index: sys/netinet/pim.h
===================================================================
--- sys/netinet/pim.h
+++ sys/netinet/pim.h
@@ -71,7 +71,7 @@
 #endif /* ! _PIM_VT  */
 	uint8_t		pim_reserved;	/* Reserved			*/
 	uint16_t	pim_cksum;	/* IP-style checksum		*/
-};
+} __packed;
 /* KAME-related name backward compatibility */
 #define pim_ver pim_vers
 #define pim_rsv pim_reserved
Index: sys/netinet/tcp.h
===================================================================
--- sys/netinet/tcp.h
+++ sys/netinet/tcp.h
@@ -77,7 +77,7 @@
 	u_short	th_win;			/* window */
 	u_short	th_sum;			/* checksum */
 	u_short	th_urp;			/* urgent pointer */
-};
+} __packed;
 
 static __inline uint16_t
 __tcp_get_flags(const struct tcphdr *th)
Index: sys/netinet/udp.h
===================================================================
--- sys/netinet/udp.h
+++ sys/netinet/udp.h
@@ -44,7 +44,7 @@
 	u_short	uh_dport;		/* destination port */
 	u_short	uh_ulen;		/* udp length */
 	u_short	uh_sum;			/* udp checksum */
-};
+} __packed;
 
 /*
  * User-settable options (used with setsockopt).
Index: tests/sys/netinet/ip_reass_test.c
===================================================================
--- tests/sys/netinet/ip_reass_test.c
+++ tests/sys/netinet/ip_reass_test.c
@@ -60,12 +60,16 @@
 {
 	size_t i;
 	uint32_t cksum;
-	uint16_t *cksump;
+	uint8_t  *cksump;
+	uint16_t tmp;
 
 	ip->ip_sum = 0;
-	cksump = (uint16_t *)ip;
-	for (cksum = 0, i = 0; i < sizeof(*ip) / sizeof(*cksump); cksump++, i++)
-		cksum += ntohs(*cksump);
+	cksump = (char *)ip;
+	for (cksum = 0, i = 0; i < sizeof(*ip) / sizeof(uint16_t); i++) {
+		tmp = *cksump++;
+		tmp = tmp << 8 | *cksump++;
+		cksum += ntohs(tmp);
+	}
 	cksum = (cksum >> 16) + (cksum & 0xffff);
 	cksum = ~(cksum + (cksum >> 16));
 	ip->ip_sum = htons((uint16_t)cksum);