diff --git a/ext/assrender/gstassrender.c b/ext/assrender/gstassrender.c
index 9cfe9970d6..771be41d11 100644
--- a/ext/assrender/gstassrender.c
+++ b/ext/assrender/gstassrender.c
@@ -234,6 +234,7 @@ gst_ass_render_init (GstAssRender * render, GstAssRenderClass * gclass)
   gst_segment_init (&render->video_segment, GST_FORMAT_TIME);
   gst_segment_init (&render->subtitle_segment, GST_FORMAT_TIME);
 
+  render->ass_mutex = g_mutex_new ();
   render->ass_library = ass_library_init ();
 #if defined(LIBASS_VERSION) && LIBASS_VERSION >= 0x00907000
   ass_set_message_cb (render->ass_library, _libass_message_cb, render);
@@ -274,6 +275,9 @@ gst_ass_render_finalize (GObject * object)
     ass_library_done (render->ass_library);
   }
 
+  if (render->ass_mutex)
+    g_mutex_free (render->ass_mutex);
+
   G_OBJECT_CLASS (parent_class)->finalize (object);
 }
 
@@ -289,7 +293,9 @@ gst_ass_render_set_property (GObject * object, guint prop_id,
       break;
     case PROP_EMBEDDEDFONTS:
       render->embeddedfonts = g_value_get_boolean (value);
+      g_mutex_lock (render->ass_mutex);
       ass_set_extract_fonts (render->ass_library, render->embeddedfonts);
+      g_mutex_unlock (render->ass_mutex);
       break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
@@ -348,9 +354,11 @@ gst_ass_render_change_state (GstElement * element, GstStateChange transition)
 
   switch (transition) {
     case GST_STATE_CHANGE_PAUSED_TO_READY:
+      g_mutex_lock (render->ass_mutex);
       if (render->ass_track)
         ass_free_track (render->ass_track);
       render->ass_track = NULL;
+      g_mutex_unlock (render->ass_mutex);
       render->track_init_ok = FALSE;
       render->renderer_init_ok = FALSE;
       break;
@@ -781,6 +789,7 @@ gst_ass_render_setcaps_video (GstPad * pad, GstCaps * caps)
       goto out;
   }
 
+  g_mutex_lock (render->ass_mutex);
   ass_set_frame_size (render->ass_renderer, render->width, render->height);
 
   dar = (((gdouble) par_n) * ((gdouble) render->width))
@@ -803,6 +812,7 @@ gst_ass_render_setcaps_video (GstPad * pad, GstCaps * caps)
 #endif
   ass_set_margins (render->ass_renderer, 0, 0, 0, 0);
   ass_set_use_margins (render->ass_renderer, 0);
+  g_mutex_unlock (render->ass_mutex);
 
   render->renderer_init_ok = TRUE;
 
@@ -832,6 +842,7 @@ gst_ass_render_setcaps_text (GstPad * pad, GstCaps * caps)
 
   value = gst_structure_get_value (structure, "codec_data");
 
+  g_mutex_lock (render->ass_mutex);
   if (value != NULL) {
     priv = gst_value_get_buffer (value);
     g_return_val_if_fail (priv != NULL, FALSE);
@@ -857,6 +868,7 @@ gst_ass_render_setcaps_text (GstPad * pad, GstCaps * caps)
 
     ret = TRUE;
   }
+  g_mutex_unlock (render->ass_mutex);
 
   gst_object_unref (render);
 
@@ -881,7 +893,9 @@ gst_ass_render_process_text (GstAssRender * render, GstBuffer * buffer,
       "Processing subtitles with running time %" GST_TIME_FORMAT
       " and duration %" GST_TIME_FORMAT, GST_TIME_ARGS (running_time),
       GST_TIME_ARGS (duration));
+  g_mutex_lock (render->ass_mutex);
   ass_process_chunk (render->ass_track, data, size, pts_start, pts_end);
+  g_mutex_unlock (render->ass_mutex);
   gst_buffer_unref (buffer);
 }
 
@@ -1008,6 +1022,7 @@ gst_ass_render_chain_video (GstPad * pad, GstBuffer * buffer)
     /* libass needs timestamps in ms */
     timestamp = running_time / GST_MSECOND;
 
+    g_mutex_lock (render->ass_mutex);
 #ifndef GST_DISABLE_GST_DEBUG
     /* only for testing right now. could possibly be used for optimizations? */
     step = ass_step_sub (render->ass_track, timestamp, 1);
@@ -1019,6 +1034,7 @@ gst_ass_render_chain_video (GstPad * pad, GstBuffer * buffer)
     /* not sure what the last parameter to this call is for (detect_change) */
     ass_image = ass_render_frame (render->ass_renderer, render->ass_track,
         timestamp, NULL);
+    g_mutex_unlock (render->ass_mutex);
 
     if (ass_image != NULL) {
       buffer = gst_buffer_make_writable (buffer);
@@ -1185,9 +1201,11 @@ gst_ass_render_handle_tags (GstAssRender * render, GstTagList * taglist)
       }
 
       if (valid_mimetype || valid_extension) {
+        g_mutex_lock (render->ass_mutex);
         ass_add_font (render->ass_library, (gchar *) filename,
             (gchar *) GST_BUFFER_DATA (buf), GST_BUFFER_SIZE (buf));
         GST_DEBUG_OBJECT (render, "registered new font %s", filename);
+        g_mutex_unlock (render->ass_mutex);
       }
     }
   }
@@ -1307,17 +1325,17 @@ gst_ass_render_event_text (GstPad * pad, GstEvent * event)
       break;
     case GST_EVENT_FLUSH_START:
       GST_DEBUG_OBJECT (render, "begin flushing");
+      g_mutex_lock (render->ass_mutex);
       if (render->ass_track) {
-        GST_OBJECT_LOCK (render);
         /* delete any events on the ass_track */
         for (i = 0; i < render->ass_track->n_events; i++) {
           GST_DEBUG_OBJECT (render, "deleted event with eid %i", i);
           ass_free_event (render->ass_track, i);
         }
         render->ass_track->n_events = 0;
-        GST_OBJECT_UNLOCK (render);
         GST_DEBUG_OBJECT (render, "done flushing");
       }
+      g_mutex_unlock (render->ass_mutex);
       g_mutex_lock (render->subtitle_mutex);
       if (render->subtitle_pending)
         gst_buffer_unref (render->subtitle_pending);
diff --git a/ext/assrender/gstassrender.h b/ext/assrender/gstassrender.h
index 72fa7bb584..4b58e25888 100644
--- a/ext/assrender/gstassrender.h
+++ b/ext/assrender/gstassrender.h
@@ -68,6 +68,7 @@ struct _GstAssRender
   gboolean subtitle_flushing;
   GstSegment subtitle_segment;
 
+  GMutex *ass_mutex;
   ASS_Library *ass_library;
   ASS_Renderer *ass_renderer;
   ASS_Track *ass_track;