diff --git a/master/master.c b/master/master.c
index eed47ff4ae7bf07435c5a1123dc3258f32d394fe..276c2e31b6cacc2278da4d2eeb8d2b8c46b5a6f8 100644
--- a/master/master.c
+++ b/master/master.c
@@ -433,6 +433,7 @@ void ec_master_leave_operation_mode(ec_master_t *master
 
     // set states for all slaves
     list_for_each_entry(slave, &master->slaves, list) {
+        ec_slave_reset(slave);
         ec_slave_request_state(slave, EC_SLAVE_STATE_PREOP);
 
         fsm->slave = slave;
@@ -452,10 +453,6 @@ void ec_master_leave_operation_mode(ec_master_t *master
     master->release_cb = NULL;
     master->cb_data = NULL;
 
-    list_for_each_entry(slave, &master->slaves, list) {
-        ec_slave_reset(slave);
-    }
-
     master->mode = EC_MASTER_MODE_IDLE;
     queue_delayed_work(master->workqueue, &master->idle_work, 1);
 }
diff --git a/master/slave.c b/master/slave.c
index 95aa8b4f5fc5f77e59349d5c843e1a595718efa9..6d9497e20c43ee8b49560f8c8c46713c16c179e7 100644
--- a/master/slave.c
+++ b/master/slave.c
@@ -284,6 +284,7 @@ void ec_slave_clear(struct kobject *kobj /**< kobject of the slave */)
 void ec_slave_reset(ec_slave_t *slave /**< EtherCAT slave */)
 {
     ec_sdo_data_t *sdodata, *next_sdodata;
+    ec_sii_sync_t *sync;
 
     // remove FMMU configurations
     slave->fmmu_count = 0;
@@ -294,6 +295,11 @@ void ec_slave_reset(ec_slave_t *slave /**< EtherCAT slave */)
         kfree(sdodata->data);
         kfree(sdodata);
     }
+
+    // remove estimated sync manager sizes
+    list_for_each_entry(sync, &slave->sii_syncs, list) {
+        sync->est_length = 0;
+    }
 }
 
 /*****************************************************************************/