diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index b9234d37..08b6b552 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -309,9 +309,11 @@
 /**
  * MEMP_NUM_SYS_TIMEOUT: the number of simulateously active timeouts.
  * (requires NO_SYS==0)
+ * The default number of timeouts is calculated here for all enabled modules.
+ * The formula expects settings to be either '0' or '1'.
  */
 #ifndef MEMP_NUM_SYS_TIMEOUT
-#define MEMP_NUM_SYS_TIMEOUT            3
+#define MEMP_NUM_SYS_TIMEOUT            (LWIP_TCP + IP_REASSEMBLY + LWIP_ARP + (2*LWIP_DHCP) + LWIP_AUTOIP + LWIP_IGMP + LWIP_DNS + PPP_SUPPORT + (LWIP_IPV6 ? (1 + LWIP_IPV6_REASS + LWIP_IPV6_MLD) : 0))
 #endif
 
 /**