diff --git a/CHANGELOG b/CHANGELOG
index 46b807e6..b56b661a 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -211,6 +211,10 @@ HISTORY
 
   ++ Bugfixes:
 
+  2010-05-16: Simon Goldschmidt
+  * def.h/.c: changed the semantics of LWIP_PREFIX_BYTEORDER_FUNCS to prevent
+    "symbol already defined" i.e. when linking to winsock
+
   2010-05-05: Simon Goldschmidt
   * def.h, timers.c: Fixed bug #29769 (sys_check_timeouts: sys_now() may
     overflow)
diff --git a/src/core/def.c b/src/core/def.c
index 003daedf..352b5524 100644
--- a/src/core/def.c
+++ b/src/core/def.c
@@ -61,7 +61,7 @@
  * @return n in network byte order
  */
 u16_t
-htons(u16_t n)
+lwip_htons(u16_t n)
 {
   return ((n & 0xff) << 8) | ((n & 0xff00) >> 8);
 }
@@ -73,9 +73,9 @@ htons(u16_t n)
  * @return n in host byte order
  */
 u16_t
-ntohs(u16_t n)
+lwip_ntohs(u16_t n)
 {
-  return htons(n);
+  return lwip_htons(n);
 }
 
 /**
@@ -85,7 +85,7 @@ ntohs(u16_t n)
  * @return n in network byte order
  */
 u32_t
-htonl(u32_t n)
+lwip_htonl(u32_t n)
 {
   return ((n & 0xff) << 24) |
     ((n & 0xff00) << 8) |
@@ -100,9 +100,9 @@ htonl(u32_t n)
  * @return n in host byte order
  */
 u32_t
-ntohl(u32_t n)
+lwip_ntohl(u32_t n)
 {
-  return htonl(n);
+  return lwip_htonl(n);
 }
 
 #endif /* (LWIP_PLATFORM_BYTESWAP == 0) && (BYTE_ORDER == LITTLE_ENDIAN) */
diff --git a/src/include/lwip/def.h b/src/include/lwip/def.h
index cda5d820..9c06ea63 100644
--- a/src/include/lwip/def.h
+++ b/src/include/lwip/def.h
@@ -58,6 +58,13 @@ extern "C" {
 #define LWIP_MAKE_U16(a, b) ((b << 8) | a)
 #endif 
 
+#ifndef LWIP_PLATFORM_BYTESWAP
+#define LWIP_PLATFORM_BYTESWAP 0
+#endif
+
+#ifndef LWIP_PREFIX_BYTEORDER_FUNCS
+/* workaround for naming collisions on some platforms */
+
 #ifdef htons
 #undef htons
 #endif /* htons */
@@ -71,33 +78,28 @@ extern "C" {
 #undef ntohl
 #endif /* ntohl */
 
-#ifndef LWIP_PLATFORM_BYTESWAP
-#define LWIP_PLATFORM_BYTESWAP 0
-#endif
+#define htons(x) lwip_htons(x)
+#define ntohs(x) lwip_ntohs(x)
+#define htonl(x) lwip_htonl(x)
+#define ntohl(x) lwip_ntohl(x)
+#endif /* LWIP_PREFIX_BYTEORDER_FUNCS */
 
 #if BYTE_ORDER == BIG_ENDIAN
-#define htons(x) (x)
-#define ntohs(x) (x)
-#define htonl(x) (x)
-#define ntohl(x) (x)
+#define lwip_htons(x) (x)
+#define lwip_ntohs(x) (x)
+#define lwip_htonl(x) (x)
+#define lwip_ntohl(x) (x)
 #else /* BYTE_ORDER != BIG_ENDIAN */
-#ifdef LWIP_PREFIX_BYTEORDER_FUNCS
-/* workaround for naming collisions on some platforms */
-#define htons lwip_htons
-#define ntohs lwip_ntohs
-#define htonl lwip_htonl
-#define ntohl lwip_ntohl
-#endif /* LWIP_PREFIX_BYTEORDER_FUNCS */
 #if LWIP_PLATFORM_BYTESWAP
-#define htons(x) LWIP_PLATFORM_HTONS(x)
-#define ntohs(x) LWIP_PLATFORM_HTONS(x)
-#define htonl(x) LWIP_PLATFORM_HTONL(x)
-#define ntohl(x) LWIP_PLATFORM_HTONL(x)
+#define lwip_htons(x) LWIP_PLATFORM_HTONS(x)
+#define lwip_ntohs(x) LWIP_PLATFORM_HTONS(x)
+#define lwip_htonl(x) LWIP_PLATFORM_HTONL(x)
+#define lwip_ntohl(x) LWIP_PLATFORM_HTONL(x)
 #else /* LWIP_PLATFORM_BYTESWAP */
-u16_t htons(u16_t x);
-u16_t ntohs(u16_t x);
-u32_t htonl(u32_t x);
-u32_t ntohl(u32_t x);
+u16_t lwip_htons(u16_t x);
+u16_t lwip_ntohs(u16_t x);
+u32_t lwip_htonl(u32_t x);
+u32_t lwip_ntohl(u32_t x);
 #endif /* LWIP_PLATFORM_BYTESWAP */
 
 #endif /* BYTE_ORDER == BIG_ENDIAN */