diff --git a/CHANGELOG b/CHANGELOG
index 8f0f5ba3..77da0cff 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -198,6 +198,10 @@ HISTORY
 
   ++ Bugfixes:
 
+  2010-05-05: Simon Goldschmidt
+  * def.h, timers.c: Fixed bug #29769 (sys_check_timeouts: sys_now() may
+    overflow)
+
   2010-04-21: Simon Goldschmidt
   * api_msg.c: Fixed bug #29617 (sometime cause stall on delete listening
     connection)
diff --git a/src/core/timers.c b/src/core/timers.c
index 433e4adb..0dba9272 100644
--- a/src/core/timers.c
+++ b/src/core/timers.c
@@ -370,8 +370,8 @@ sys_check_timeouts(void)
 
   now = sys_now();
   if (next_timeout) {
-    /* @todo: wrap around? */
-    diff = now - timeouts_last_time;
+    /* this cares for wraparounds */
+    diff = LWIP_U32_DIFF(now, timeouts_last_time);
     do
     {
       had_one = 0;
diff --git a/src/include/lwip/def.h b/src/include/lwip/def.h
index 52d511af..cda5d820 100644
--- a/src/include/lwip/def.h
+++ b/src/include/lwip/def.h
@@ -47,6 +47,11 @@ extern "C" {
 #define NULL ((void *)0)
 #endif
 
+/** Get the absolute difference between 2 u32_t values (correcting overflows)
+ * 'a' is expected to be 'higher' (without overflow) than 'b'. */
+#define LWIP_U32_DIFF(a, b) (((a) >= (b)) ? ((a) - (b)) : (((a) + ((b) ^ 0xFFFFFFFF) + 1))) 
+
+/* Endianess-optimized shifting of two u8_t to create one u16_t */
 #if BYTE_ORDER == LITTLE_ENDIAN
 #define LWIP_MAKE_U16(a, b) ((a << 8) | b)
 #else