diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 4626a158..858fc240 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -461,7 +461,7 @@
  * The number of sys timeouts used by the core stack (not apps)
  * The default number of timeouts is calculated here for all enabled modules.
  */
-#define LWIP_NUM_SYS_TIMEOUT_INTERNAL   (LWIP_TCP + IP_REASSEMBLY + LWIP_ARP + (2*LWIP_DHCP) + LWIP_AUTOIP + LWIP_IGMP + LWIP_DNS + (PPP_SUPPORT*6*MEMP_NUM_PPP_PCB) + (LWIP_IPV6 ? (1 + LWIP_IPV6_REASS + LWIP_IPV6_MLD) : 0))
+#define LWIP_NUM_SYS_TIMEOUT_INTERNAL   (LWIP_TCP + IP_REASSEMBLY + LWIP_ARP + (2*LWIP_DHCP) + LWIP_AUTOIP + LWIP_IGMP + LWIP_DNS + PPP_NUM_TIMEOUTS + (LWIP_IPV6 * (1 + LWIP_IPV6_REASS + LWIP_IPV6_MLD)))
 
 /**
  * MEMP_NUM_SYS_TIMEOUT: the number of simultaneously active timeouts.
diff --git a/src/include/netif/ppp/ppp_opts.h b/src/include/netif/ppp/ppp_opts.h
index fa79c090..c987c110 100644
--- a/src/include/netif/ppp/ppp_opts.h
+++ b/src/include/netif/ppp/ppp_opts.h
@@ -77,9 +77,20 @@
  * connections (requires the PPP_SUPPORT option)
  */
 #ifndef MEMP_NUM_PPP_PCB
-#define MEMP_NUM_PPP_PCB       1
+#define MEMP_NUM_PPP_PCB                1
 #endif
 
+/**
+ * PPP_NUM_TIMEOUTS_PER_PCB: the number of sys_timeouts running in parallel per
+ * ppp_pcb. This is a conservative default which needs to be checked...
+ */
+#ifndef PPP_NUM_TIMEOUTS_PER_PCB
+#define PPP_NUM_TIMEOUTS_PER_PCB        6
+#endif
+
+/* The number of sys_timeouts required for the PPP module */
+#define PPP_NUM_TIMEOUTS                (PPP_SUPPORT * PPP_NUM_TIMEOUTS_PER_PCB * MEMP_NUM_PPP_PCB)
+
 #if PPP_SUPPORT
 
 /**