diff --git a/monitor.c b/monitor.c
index a1329d8a86..d353c0e645 100644
--- a/monitor.c
+++ b/monitor.c
@@ -263,10 +263,11 @@ typedef struct QMPRequest QMPRequest;
 /* QMP checker flags */
 #define QMP_ACCEPT_UNKNOWNS 1
 
-/* Protects mon_list, monitor_qapi_event_state.  */
+/* Protects mon_list, monitor_qapi_event_state, monitor_destroyed.  */
 static QemuMutex monitor_lock;
 static GHashTable *monitor_qapi_event_state;
 static QTAILQ_HEAD(mon_list, Monitor) mon_list;
+static bool monitor_destroyed;
 
 /* Protects mon_fdsets */
 static QemuMutex mon_fdsets_lock;
@@ -4538,8 +4539,21 @@ void error_vprintf_unless_qmp(const char *fmt, va_list ap)
 static void monitor_list_append(Monitor *mon)
 {
     qemu_mutex_lock(&monitor_lock);
-    QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
+    /*
+     * This prevents inserting new monitors during monitor_cleanup().
+     * A cleaner solution would involve the main thread telling other
+     * threads to terminate, waiting for their termination.
+     */
+    if (!monitor_destroyed) {
+        QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
+        mon = NULL;
+    }
     qemu_mutex_unlock(&monitor_lock);
+
+    if (mon) {
+        monitor_data_destroy(mon);
+        g_free(mon);
+    }
 }
 
 static void monitor_qmp_setup_handlers_bh(void *opaque)
@@ -4634,6 +4648,7 @@ void monitor_cleanup(void)
 
     /* Flush output buffers and destroy monitors */
     qemu_mutex_lock(&monitor_lock);
+    monitor_destroyed = true;
     QTAILQ_FOREACH_SAFE(mon, &mon_list, entry, next) {
         QTAILQ_REMOVE(&mon_list, mon, entry);
         monitor_flush(mon);