diff --git a/src/include/lwip/dhcp.h b/src/include/lwip/dhcp.h
index 400f81fd..825dba6e 100644
--- a/src/include/lwip/dhcp.h
+++ b/src/include/lwip/dhcp.h
@@ -18,7 +18,7 @@ extern "C" {
 /** period (in seconds) of the application calling dhcp_coarse_tmr() */
 #define DHCP_COARSE_TIMER_SECS 60 
 /** period (in milliseconds) of the application calling dhcp_coarse_tmr() */
-#define DHCP_COARSE_TIMER_MSECS (DHCP_COARSE_TIMER_SECS*1000)
+#define DHCP_COARSE_TIMER_MSECS (DHCP_COARSE_TIMER_SECS * 1000UL)
 /** period (in milliseconds) of the application calling dhcp_fine_tmr() */
 #define DHCP_FINE_TIMER_MSECS 500