diff --git a/gst/avi/gstavimux.c b/gst/avi/gstavimux.c
index 8a7d843e65..17ec92db29 100644
--- a/gst/avi/gstavimux.c
+++ b/gst/avi/gstavimux.c
@@ -1166,7 +1166,10 @@ gst_avi_mux_riff_get_avi_header (GstAviMux * avimux)
   else {
     /* need to make snapshot of current state of tags to ensure the same set
      * is used next time around during header rewrite at the end */
+    /* FIXME: remove locking again after GstTagSetter has been fixed */
+    GST_OBJECT_LOCK (avimux);
     tags = gst_tag_setter_get_tag_list (GST_TAG_SETTER (avimux));
+    GST_OBJECT_UNLOCK (avimux);
     if (tags)
       tags = avimux->tags_snap = gst_tag_list_copy (tags);
   }
@@ -1919,10 +1922,15 @@ gst_avi_mux_handle_event (GstPad * pad, GstEvent * event)
     case GST_EVENT_TAG:{
       GstTagList *list;
       GstTagSetter *setter = GST_TAG_SETTER (avimux);
-      const GstTagMergeMode mode = gst_tag_setter_get_tag_merge_mode (setter);
+      GstTagMergeMode mode;
 
       gst_event_parse_tag (event, &list);
+
+      /* FIXME: remove locking again after GstTagSetter has been fixed */
+      GST_OBJECT_LOCK (avimux);
+      mode = gst_tag_setter_get_tag_merge_mode (setter);
       gst_tag_setter_merge_tags (setter, list, mode);
+      GST_OBJECT_UNLOCK (avimux);
       break;
     }
     default:
diff --git a/gst/flv/gstflvmux.c b/gst/flv/gstflvmux.c
index 883ebb7563..1addaa4b0f 100644
--- a/gst/flv/gstflvmux.c
+++ b/gst/flv/gstflvmux.c
@@ -256,10 +256,15 @@ gst_flv_mux_handle_sink_event (GstPad * pad, GstEvent * event)
     case GST_EVENT_TAG:{
       GstTagList *list;
       GstTagSetter *setter = GST_TAG_SETTER (mux);
-      const GstTagMergeMode mode = gst_tag_setter_get_tag_merge_mode (setter);
+      GstTagMergeMode mode;
 
       gst_event_parse_tag (event, &list);
+
+      /* FIXME: remove locking again after GstTagSetter has been fixed */
+      GST_OBJECT_LOCK (mux);
+      mode = gst_tag_setter_get_tag_merge_mode (setter);
       gst_tag_setter_merge_tags (setter, list, mode);
+      GST_OBJECT_UNLOCK (mux);
       break;
     }
     case GST_EVENT_NEWSEGMENT:
@@ -634,7 +639,10 @@ gst_flv_mux_create_metadata (GstFlvMux * mux)
   guint8 *data;
   gint i, n_tags, tags_written = 0;
 
+  /* FIXME: remove locking again after GstTagSetter has been fixed */
+  GST_OBJECT_LOCK (mux);
   tags = gst_tag_setter_get_tag_list (GST_TAG_SETTER (mux));
+  GST_OBJECT_UNLOCK (mux);
 
   GST_DEBUG_OBJECT (mux, "tags = %" GST_PTR_FORMAT, tags);
 
diff --git a/gst/matroska/matroska-mux.c b/gst/matroska/matroska-mux.c
index e21e763c6f..15441a183b 100644
--- a/gst/matroska/matroska-mux.c
+++ b/gst/matroska/matroska-mux.c
@@ -625,8 +625,11 @@ gst_matroska_mux_handle_sink_event (GstPad * pad, GstEvent * event)
         g_free (lang);
       }
 
+      /* FIXME: remove locking again after GstTagSetter has been fixed */
+      GST_OBJECT_LOCK (mux);
       gst_tag_setter_merge_tags (GST_TAG_SETTER (mux), list,
           gst_tag_setter_get_tag_merge_mode (GST_TAG_SETTER (mux)));
+      GST_OBJECT_UNLOCK (mux);
       break;
     }
     case GST_EVENT_NEWSEGMENT:
@@ -2205,7 +2208,10 @@ gst_matroska_mux_finish (GstMatroskaMux * mux)
   }
 
   /* tags */
+  /* FIXME: remove locking again after GstTagSetter has been fixed */
+  GST_OBJECT_LOCK (mux);
   tags = gst_tag_setter_get_tag_list (GST_TAG_SETTER (mux));
+  GST_OBJECT_UNLOCK (mux);
 
   if (tags != NULL && !gst_tag_list_is_empty (tags)) {
     guint64 master_tags, master_tag;