diff --git a/extensions/compat_xtables.c b/extensions/compat_xtables.c
index 438047a..9ab4785 100644
--- a/extensions/compat_xtables.c
+++ b/extensions/compat_xtables.c
@@ -20,11 +20,6 @@
 #include "compat_skbuff.h"
 #include "compat_xtnu.h"
 
-#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 19)
-typedef __u16 __bitwise __sum16;
-typedef __u32 __bitwise __wsum;
-#endif
-
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 22)
 static int xtnu_match_run(const struct sk_buff *skb,
     const struct net_device *in, const struct net_device *out,
@@ -452,17 +447,23 @@ void xtnu_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
     __be32 from, __be32 to, bool pseudohdr)
 {
 	__be32 diff[] = {~from, to};
+	const void *dv = diff; /* kludge for < v2.6.19-555-g72685fc */
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 19)
 	if (skb->ip_summed != CHECKSUM_PARTIAL) {
-		*sum = csum_fold(csum_partial(diff, sizeof(diff),
+		*sum = csum_fold(csum_partial(dv, sizeof(diff),
 		       ~csum_unfold(*sum)));
 		if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr)
-			skb->csum = ~csum_partial(diff, sizeof(diff),
+			skb->csum = ~csum_partial(dv, sizeof(diff),
 			            ~skb->csum);
 	} else if (pseudohdr) {
-		*sum = ~csum_fold(csum_partial(diff, sizeof(diff),
+		*sum = ~csum_fold(csum_partial(dv, sizeof(diff),
 		       csum_unfold(*sum)));
 	}
+#else
+	*sum = csum_fold(csum_partial(dv, sizeof(diff),
+	       ~csum_unfold(*sum)));
+#endif
 }
 EXPORT_SYMBOL_GPL(xtnu_proto_csum_replace4);
 #endif
diff --git a/extensions/compat_xtables.h b/extensions/compat_xtables.h
index 1187dfa..77ea3b4 100644
--- a/extensions/compat_xtables.h
+++ b/extensions/compat_xtables.h
@@ -37,6 +37,7 @@
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 19)
 #	define neigh_hh_output xtnu_neigh_hh_output
 #	define IPPROTO_UDPLITE 136
+#	define CSUM_MANGLED_0 ((__force __sum16)0xffff)
 #endif
 
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 24)
@@ -70,6 +71,7 @@
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 19)
 #	define csum_replace2 xtnu_csum_replace2
 #	define csum_replace4 xtnu_csum_replace4
+#	define inet_proto_csum_replace4 xtnu_proto_csum_replace4
 #elif LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 24)
 #	define csum_replace2 nf_csum_replace2
 #	define csum_replace4 nf_csum_replace4
diff --git a/extensions/compat_xtnu.h b/extensions/compat_xtnu.h
index 0a19082..6e6620a 100644
--- a/extensions/compat_xtnu.h
+++ b/extensions/compat_xtnu.h
@@ -9,6 +9,10 @@
 typedef _Bool bool;
 enum { false = 0, true = 1, };
 #endif
+#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 19)
+typedef __u16 __bitwise __sum16;
+typedef __u32 __bitwise __wsum;
+#endif
 
 struct flowi;
 struct hh_cache;
@@ -122,6 +126,13 @@ static inline struct xtnu_target *xtcompat_nutarget(const struct xt_target *t)
 	return q;
 }
 
+#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 19)
+static inline __wsum csum_unfold(__sum16 n)
+{
+	return (__force __wsum)n;
+}
+#endif
+
 extern int xtnu_ip_local_out(struct sk_buff *);
 extern int xtnu_ip_route_me_harder(struct sk_buff **, unsigned int);
 extern int xtnu_skb_make_writable(struct sk_buff **, unsigned int);
diff --git a/extensions/xt_RAWNAT.c b/extensions/xt_RAWNAT.c
index 6184524..18661a9 100644
--- a/extensions/xt_RAWNAT.c
+++ b/extensions/xt_RAWNAT.c
@@ -79,6 +79,7 @@ static void rawnat4_update_l4(struct sk_buff *skb, __be32 oldip, __be32 newip)
 	void *transport_hdr = (void *)iph + ip_hdrlen(skb);
 	struct tcphdr *tcph;
 	struct udphdr *udph;
+	bool cond;
 
 	switch (iph->protocol) {
 	case IPPROTO_TCP:
@@ -88,7 +89,11 @@ static void rawnat4_update_l4(struct sk_buff *skb, __be32 oldip, __be32 newip)
 	case IPPROTO_UDP:
 	case IPPROTO_UDPLITE:
 		udph = transport_hdr;
-		if (udph->check != 0 || skb->ip_summed == CHECKSUM_PARTIAL) {
+		cond = udph->check != 0;
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 19)
+		cond |= skb->ip_summed == CHECKSUM_PARTIAL;
+#endif
+		if (cond) {
 			inet_proto_csum_replace4(&udph->check, skb,
 				oldip, newip, true);
 			if (udph->check == 0)
@@ -200,6 +205,7 @@ static void rawnat6_update_l4(struct sk_buff *skb, unsigned int l4proto,
 	struct tcphdr *tcph;
 	struct udphdr *udph;
 	unsigned int i;
+	bool cond;
 
 	switch (l4proto) {
 	case IPPROTO_TCP:
@@ -211,7 +217,11 @@ static void rawnat6_update_l4(struct sk_buff *skb, unsigned int l4proto,
 	case IPPROTO_UDP:
 	case IPPROTO_UDPLITE:
 		udph = (void *)iph + l4offset;
-		if (udph->check != 0 || skb->ip_summed == CHECKSUM_PARTIAL) {
+		cond = udph->check;
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 19)
+		cond |= skb->ip_summed == CHECKSUM_PARTIAL;
+#endif
+		if (cond) {
 			for (i = 0; i < 4; ++i)
 				inet_proto_csum_replace4(&udph->check, skb,
 					oldip->s6_addr32[i],