diff --git a/subprojects/gstreamer/libs/gst/base/gstbasesrc.h b/subprojects/gstreamer/libs/gst/base/gstbasesrc.h
index b1612dcafb..4207ffc3ff 100644
--- a/subprojects/gstreamer/libs/gst/base/gstbasesrc.h
+++ b/subprojects/gstreamer/libs/gst/base/gstbasesrc.h
@@ -184,6 +184,14 @@ struct _GstBaseSrcClass {
   /* decide on caps */
   gboolean      (*negotiate)    (GstBaseSrc *src);
   /* called if, in negotiation, caps need fixating */
+  /**
+   * GstBaseSrcClass::fixate:
+   * @caps: (transfer full):
+   *
+   * Called if, in negotiation, caps need fixating.
+   *
+   * Returns: (transfer full): the fixated caps
+   */
   GstCaps *     (*fixate)       (GstBaseSrc *src, GstCaps *caps);
   /* notify the subclass of new caps */
   gboolean      (*set_caps)     (GstBaseSrc *src, GstCaps *caps);