diff --git a/esp8266/modmachine.c b/esp8266/modmachine.c
index 4a73883..afb7ba5 100644
--- a/esp8266/modmachine.c
+++ b/esp8266/modmachine.c
@@ -75,6 +75,8 @@
     mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
     self->callback = args[2].u_obj;
+    // Be sure to disarm timer before making any changes
+    os_timer_disarm(&self->timer);
     os_timer_setfn(&self->timer, esp_timer_cb, self);
     os_timer_arm(&self->timer, args[0].u_int, args[1].u_int);