diff --git a/CHANGELOG b/CHANGELOG
index aaea2727..e2cb951f 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -233,6 +233,9 @@ HISTORY
 
   ++ Bugfixes:
 
+  2011-02-17: Simon Goldschmidt
+  * ipaddr.c: Fixed constant not being 32 bit.
+
   2011-01-24: Simon Goldschmidt
   * sockets.c: Fixed bug #31741: lwip_select seems to have threading problems
 
diff --git a/src/core/ipv4/ip_addr.c b/src/core/ipv4/ip_addr.c
index 7e953d37..8f633ff2 100644
--- a/src/core/ipv4/ip_addr.c
+++ b/src/core/ipv4/ip_addr.c
@@ -93,7 +93,7 @@ ip4_addr_netmask_valid(u32_t netmask)
   u32_t nm_hostorder = lwip_htonl(netmask);
 
   /* first, check for the first zero */
-  for (mask = 1U << 31 ; mask != 0; mask >>= 1) {
+  for (mask = 1UL << 31 ; mask != 0; mask >>= 1) {
     if ((nm_hostorder & mask) == 0) {
       break;
     }