diff --git a/CHANGELOG b/CHANGELOG
index 68b275c8..3d827ca7 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -69,6 +69,10 @@ HISTORY
 
  ++ Bugfixes:
 
+  2011-11-23: Simon Goldschmidt
+  * sys.c: fixed bug #34884: sys_msleep() body needs to be surrounded with
+    '#ifndef sys_msleep'
+
   2011-11-22: Simon Goldschmidt
   * netif.c, etharp.h/.c: fixed bug #34684: Clear the arp table cache when
     netif is brought down
diff --git a/src/core/sys.c b/src/core/sys.c
index d3a77deb..f1777372 100644
--- a/src/core/sys.c
+++ b/src/core/sys.c
@@ -45,6 +45,7 @@
 
 #if !NO_SYS
 
+#ifndef sys_msleep
 /**
  * Sleep for some ms. Timeouts are NOT processed while sleeping.
  *
@@ -62,5 +63,6 @@ sys_msleep(u32_t ms)
     }
   }
 }
+#endif /* sys_msleep */
 
 #endif /* !NO_SYS */