diff --git a/ext/gl/gstglmixer.c b/ext/gl/gstglmixer.c
index 9a7446ab0b..b8f4da0267 100644
--- a/ext/gl/gstglmixer.c
+++ b/ext/gl/gstglmixer.c
@@ -224,6 +224,7 @@ _update_caps (GstVideoAggregator * vagg, GstCaps * caps, GstCaps * filter)
 
   if (filter) {
     tmp = gst_caps_intersect (caps, filter);
+    tmp = gst_caps_make_writable (tmp);
   } else {
     tmp = gst_caps_copy (caps);
   }