diff --git a/sys/netinet/libalias/alias_ftp.c b/sys/netinet/libalias/alias_ftp.c
index 2eb885944fce..d91e1cde018f 100644
--- a/sys/netinet/libalias/alias_ftp.c
+++ b/sys/netinet/libalias/alias_ftp.c
@@ -677,7 +677,11 @@ NewFtpMessage(struct libalias *la, struct ip *pip,
 
 /* Compute TCP checksum for revised packet */
 		tc->th_sum = 0;
+#ifdef _KERNEL
+		tc->th_x2 = 1;
+#else
 		tc->th_sum = TcpChecksum(pip);
+#endif
 	} else {
 #ifdef LIBALIAS_DEBUG
 		fprintf(stderr,
diff --git a/sys/netinet/libalias/alias_irc.c b/sys/netinet/libalias/alias_irc.c
index 6d8bf3dd051d..defdb561384e 100644
--- a/sys/netinet/libalias/alias_irc.c
+++ b/sys/netinet/libalias/alias_irc.c
@@ -374,7 +374,11 @@ lPACKET_DONE:
 
 		/* Compute TCP checksum for revised packet */
 		tc->th_sum = 0;
+#ifdef _KERNEL
+		tc->th_x2 = 1;
+#else
 		tc->th_sum = TcpChecksum(pip);
+#endif
 		return;
 	}
 }
diff --git a/sys/netinet/libalias/alias_local.h b/sys/netinet/libalias/alias_local.h
index 63f6288fb67b..4dc2e0a95742 100644
--- a/sys/netinet/libalias/alias_local.h
+++ b/sys/netinet/libalias/alias_local.h
@@ -178,9 +178,18 @@ struct libalias {
 
 /* Prototypes */
 
-/* General utilities */
+/*
+ * We do not calculate TCP checksums when libalias is a kernel
+ * module, since it has no idea about checksum offloading.
+ * If TCP data has changed, then we just set checksum to zero,
+ * and caller must recalculate it himself.
+ * In case if libalias will edit UDP data, the same approach
+ * should be used.
+ */
+#ifndef _KERNEL
 u_short		IpChecksum(struct ip *_pip);
 u_short		TcpChecksum(struct ip *_pip);
+#endif
 void
 DifferentialChecksum(u_short * _cksum, void * _new, void * _old, int _n);
 
diff --git a/sys/netinet/libalias/alias_proxy.c b/sys/netinet/libalias/alias_proxy.c
index b2789f36ec13..f683ba095240 100644
--- a/sys/netinet/libalias/alias_proxy.c
+++ b/sys/netinet/libalias/alias_proxy.c
@@ -474,7 +474,11 @@ ProxyEncodeTcpStream(struct alias_link *lnk,
    already changed. */
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
+#endif
 }
 
 static void
diff --git a/sys/netinet/libalias/alias_skinny.c b/sys/netinet/libalias/alias_skinny.c
index 4493b1b45142..f109f74c4d65 100644
--- a/sys/netinet/libalias/alias_skinny.c
+++ b/sys/netinet/libalias/alias_skinny.c
@@ -150,7 +150,11 @@ alias_skinny_reg_msg(struct RegisterMessage *reg_msg, struct ip *pip,
 	reg_msg->ipAddr = (u_int32_t) GetAliasAddress(lnk).s_addr;
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
+#endif
 
 	return (0);
 }
@@ -189,8 +193,11 @@ alias_skinny_port_msg(struct IpPortMessage *port_msg, struct ip *pip,
 	port_msg->stationIpPort = (u_int32_t) ntohs(GetAliasPort(lnk));
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
-
+#endif
 	return (0);
 }
 
@@ -218,8 +225,11 @@ alias_skinny_opnrcvch_ack(struct libalias *la, struct OpenReceiveChannelAck *opn
 	opnrcvch_ack->port = (u_int32_t) ntohs(GetAliasPort(opnrcv_lnk));
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
-
+#endif
 	return (0);
 }
 
diff --git a/sys/netinet/libalias/alias_smedia.c b/sys/netinet/libalias/alias_smedia.c
index 61848bb1d4ec..c314a65f770d 100644
--- a/sys/netinet/libalias/alias_smedia.c
+++ b/sys/netinet/libalias/alias_smedia.c
@@ -331,8 +331,11 @@ alias_rtsp_out(struct libalias *la, struct ip *pip,
 	pip->ip_len = new_len;
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
-
+#endif
 	return (0);
 }
 
@@ -376,7 +379,11 @@ alias_pna_out(struct libalias *la, struct ip *pip,
 
 				/* Compute TCP checksum for revised packet */
 				tc->th_sum = 0;
+#ifdef _KERNEL
+				tc->th_x2 = 1;
+#else
 				tc->th_sum = TcpChecksum(pip);
+#endif
 			}
 		}
 		work += ntohs(msg_len);
diff --git a/sys/netinet/libalias/alias_util.c b/sys/netinet/libalias/alias_util.c
index 4234276921e2..dc70bc12667e 100644
--- a/sys/netinet/libalias/alias_util.c
+++ b/sys/netinet/libalias/alias_util.c
@@ -43,13 +43,6 @@ __FBSDID("$FreeBSD$");
 	 Added differential checksum update function.
 */
 
-/*
-Note: the checksum routines assume that the actual checksum word has
-been zeroed out.  If the checksum word is filled with the proper value,
-then these routines will give a result of zero (useful for testing
-purposes);
-*/
-
 #ifdef _KERNEL
 #include <sys/param.h>
 #else
@@ -70,6 +63,12 @@ purposes);
 #include "alias_local.h"
 #endif
 
+/*
+ * Note: the checksum routines assume that the actual checksum word has
+ * been zeroed out.  If the checksum word is filled with the proper value,
+ * then these routines will give a result of zero (useful for testing
+ * purposes);
+ */
 u_short
 LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr,
 	int nbytes)
@@ -92,6 +91,7 @@ LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr,
 	return (~sum);
 }
 
+#ifndef	_KERNEL
 u_short
 IpChecksum(struct ip *pip)
 {
@@ -144,7 +144,7 @@ TcpChecksum(struct ip *pip)
 /* Return checksum */
 	return ((u_short) ~ sum);
 }
-
+#endif	/* not _KERNEL */
 
 void
 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n)