diff --git a/.github/workflows/ci-linux.yml b/.github/workflows/ci-linux.yml
index 8ecb12f9..8b5d9bfa 100644
--- a/.github/workflows/ci-linux.yml
+++ b/.github/workflows/ci-linux.yml
@@ -51,7 +51,7 @@ jobs:
       run: |
         cp ${CONTRIB}/examples/example_app/lwipcfg.h.example ${CONTRIB}/examples/example_app/lwipcfg.h
         cd ${CONTRIB}/ports/unix/example_app
-        export CFLAGS="-DESP_LWIP=LWIP_NETCONN_FULLDUPLEX -DESP_LWIP_DNS_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_DHCP_FINE_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_IGMP_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_MLD6_TIMERS_ONDEMAND=ESP_LWIP -DESP_DNS=ESP_LWIP -DESP_LWIP_ARP=ESP_LWIP"
+        export CFLAGS="-DESP_LWIP=LWIP_NETCONN_FULLDUPLEX -DESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_DNS_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_DHCP_FINE_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_IGMP_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_MLD6_TIMERS_ONDEMAND=ESP_LWIP -DESP_DNS=ESP_LWIP -DESP_LWIP_ARP=ESP_LWIP"
         export LWIPDIR=../../../../src/
         make TESTFLAGS="-Wno-documentation" -j 4
         chmod +x iteropts.sh && ./iteropts.sh
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 88ca1ba5..d908ee84 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -86,7 +86,7 @@ validate_opts:
     - *get_contrib
     - cp ${CONTRIB}/examples/example_app/lwipcfg.h.example ${CONTRIB}/examples/example_app/lwipcfg.h
     - cd ${CONTRIB}/ports/unix/example_app
-    - export CFLAGS="-DESP_LWIP=LWIP_NETCONN_FULLDUPLEX -DESP_LWIP_DNS_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_DHCP_FINE_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_IGMP_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_MLD6_TIMERS_ONDEMAND=ESP_LWIP -DESP_DNS=ESP_LWIP"
+    - export CFLAGS="-DESP_LWIP=LWIP_NETCONN_FULLDUPLEX -DESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_DNS_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_DHCP_FINE_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_IGMP_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_MLD6_TIMERS_ONDEMAND=ESP_LWIP -DESP_DNS=ESP_LWIP"
     - export LWIPDIR=../../../../src/
     - chmod +x iteropts.sh && ./iteropts.sh
 
diff --git a/src/core/ipv4/ip4_frag.c b/src/core/ipv4/ip4_frag.c
index a445530e..39459b6a 100644
--- a/src/core/ipv4/ip4_frag.c
+++ b/src/core/ipv4/ip4_frag.c
@@ -52,6 +52,13 @@
 #include <string.h>
 
 #if IP_REASSEMBLY
+
+#if ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
+#include "lwip/timeouts.h"
+#include "stdbool.h"
+static bool s_is_tmr_start = false;
+#endif /* ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND */
+
 /**
  * The IP reassembly code currently has the following limitations:
  * - IP header options are not supported
@@ -118,6 +125,17 @@ static u16_t ip_reass_pbufcount;
 static void ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
 static int ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);
 
+#if ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
+/**
+ * Wrapper function with matching prototype which calls the actual callback
+ */
+static void ip_reass_timeout_cb(void *arg)
+{
+  LWIP_UNUSED_ARG(arg);
+  ip_reass_tmr();
+}
+#endif
+
 /**
  * Reassembly timer base function
  * for both NO_SYS == 0 and 1 (!).
@@ -128,6 +146,9 @@ void
 ip_reass_tmr(void)
 {
   struct ip_reassdata *r, *prev = NULL;
+#if ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
+  bool tmr_restart = false;
+#endif /* ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND */
 
   r = reassdatagrams;
   while (r != NULL) {
@@ -138,6 +159,9 @@ ip_reass_tmr(void)
       LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer dec %"U16_F"\n", (u16_t)r->timer));
       prev = r;
       r = r->next;
+#if ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
+      tmr_restart = true;
+#endif /* ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND */
     } else {
       /* reassembly timed out */
       struct ip_reassdata *tmp;
@@ -149,6 +173,14 @@ ip_reass_tmr(void)
       ip_reass_free_complete_datagram(tmp, prev);
     }
   }
+#if ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
+  if (tmr_restart) {
+    sys_timeout(IP_TMR_INTERVAL, ip_reass_timeout_cb, NULL);
+  } else {
+    sys_untimeout(ip_reass_timeout_cb, NULL);
+    s_is_tmr_start = false;
+  }
+#endif/* ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND */
 }
 
 /**
@@ -672,6 +704,12 @@ ip4_reass(struct pbuf *p)
     /* Return the pbuf chain */
     return p;
   }
+#if ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND 
+  if (!s_is_tmr_start) {
+    sys_timeout(IP_TMR_INTERVAL, ip_reass_timeout_cb, NULL);
+    s_is_tmr_start = true;
+  }
+#endif /* ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND */
   /* the datagram is not (yet?) reassembled completely */
   LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_pbufcount: %d out\n", ip_reass_pbufcount));
   return NULL;
diff --git a/src/core/timeouts.c b/src/core/timeouts.c
index 1391a710..d10a12cd 100644
--- a/src/core/timeouts.c
+++ b/src/core/timeouts.c
@@ -81,7 +81,7 @@ const struct lwip_cyclic_timer lwip_cyclic_timers[] = {
   {TCP_TMR_INTERVAL, HANDLER(tcp_tmr)},
 #endif /* LWIP_TCP */
 #if LWIP_IPV4
-#if IP_REASSEMBLY
+#if IP_REASSEMBLY && !ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
   {IP_TMR_INTERVAL, HANDLER(ip_reass_tmr)},
 #endif /* IP_REASSEMBLY */
 #if LWIP_ARP
diff --git a/test/apps/lwipopts.h b/test/apps/lwipopts.h
index 0cce2831..37d822ba 100644
--- a/test/apps/lwipopts.h
+++ b/test/apps/lwipopts.h
@@ -297,6 +297,9 @@ void sys_thread_sem_deinit(void);
 #define ESP_LWIP_DHCP_FINE_TIMERS_ONDEMAND 1
 #define ESP_LWIP_DNS_TIMERS_ONDEMAND  1
 #define ESP_LWIP_MLD6_TIMERS_ONDEMAND 1
+#if IP_REASSEMBLY
+#define ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND 1
+#endif /* IP_REASSEMBLY */
 #define ESP_DNS 1
 #define ESP_LWIP_ARP 1
 #define LWIP_AUTOIP_MAX_CONFLICTS        10
diff --git a/test/unit/lwipopts.h b/test/unit/lwipopts.h
index 50675a91..3ccb4314 100644
--- a/test/unit/lwipopts.h
+++ b/test/unit/lwipopts.h
@@ -162,6 +162,7 @@ u32_t esp_random(void);
 #define ESP_LWIP_MLD6_TIMERS_ONDEMAND           1
 #define ESP_LWIP_DHCP_FINE_TIMERS_ONDEMAND      1
 #define ESP_LWIP_DNS_TIMERS_ONDEMAND            1
+#define ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND 1
 
 #else
 #define ESP_LWIP                                0
@@ -177,6 +178,10 @@ u32_t esp_random(void);
 #define ESP_LWIP_DNS_TIMERS_ONDEMAND            0
 #endif
 
+#ifndef ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND
+#define ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND 0
+#endif /* ESP_LWIP_IP4_REASSEMBLY_TIMERS_ONDEMAND */
+
 #endif /* ESP_LWIP */
 
 #endif /* LWIP_HDR_LWIPOPTS_H */