diff --git a/contrib/ports/unix/port/sys_arch.c b/contrib/ports/unix/port/sys_arch.c
index 070c6cff..a56d7de1 100644
--- a/contrib/ports/unix/port/sys_arch.c
+++ b/contrib/ports/unix/port/sys_arch.c
@@ -71,7 +71,7 @@
 u32_t
 lwip_port_rand(void)
 {
-  return rand();
+  return (u32_t)rand();
 }
 
 static void