diff --git a/mongoose.c b/mongoose.c
index 37cec3da..fa15b329 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -2809,6 +2809,7 @@ void mg_mgr_free(struct mg_mgr *mgr) {
   struct mg_connection *c;
   struct mg_timer *tmp, *t = mgr->timers;
   while (t != NULL) tmp = t->next, free(t), t = tmp;
+  mgr->timers = NULL;  // Important. Next call to poll won't touch timers
   for (c = mgr->conns; c != NULL; c = c->next) c->is_closing = 1;
   mg_mgr_poll(mgr, 0);
 #if MG_ARCH == MG_ARCH_FREERTOS_TCP
diff --git a/src/net.c b/src/net.c
index 14fde456..d2333cd5 100644
--- a/src/net.c
+++ b/src/net.c
@@ -230,6 +230,7 @@ void mg_mgr_free(struct mg_mgr *mgr) {
   struct mg_connection *c;
   struct mg_timer *tmp, *t = mgr->timers;
   while (t != NULL) tmp = t->next, free(t), t = tmp;
+  mgr->timers = NULL;  // Important. Next call to poll won't touch timers
   for (c = mgr->conns; c != NULL; c = c->next) c->is_closing = 1;
   mg_mgr_poll(mgr, 0);
 #if MG_ARCH == MG_ARCH_FREERTOS_TCP
diff --git a/test/unit_test.c b/test/unit_test.c
index 5ab03407..8bb76875 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -1262,6 +1262,15 @@ static void test_timer(void) {
 
   mg_timer_free(&head, &t3);
   ASSERT(head == NULL);
+
+  // Test proper timer deallocation, see #1539
+  {
+    struct mg_mgr mgr;
+    mg_mgr_init(&mgr);
+    mg_timer_add(&mgr, 1, MG_TIMER_REPEAT, f1, NULL);
+    mg_mgr_free(&mgr);
+    ASSERT(mgr.conns == NULL);
+  }
 }
 
 static bool sn(const char *fmt, ...) {