diff --git a/gst/isomp4/gstqtmux.c b/gst/isomp4/gstqtmux.c
index 4733bb6fe7..cf8148d513 100644
--- a/gst/isomp4/gstqtmux.c
+++ b/gst/isomp4/gstqtmux.c
@@ -2968,6 +2968,10 @@ gst_qt_mux_start_file (GstQTMux * qtmux)
             (NULL));
         return GST_FLOW_ERROR;
       }
+      if (qtmux->reserved_moov_update_period == GST_CLOCK_TIME_NONE) {
+        GST_WARNING_OBJECT (qtmux,
+            "Robust muxing requires reserved-moov-update-period to be set");
+      }
       break;
     case GST_QT_MUX_MODE_FAST_START:
     case GST_QT_MUX_MODE_FRAGMENTED_STREAMABLE:
diff --git a/gst/multifile/gstsplitmuxsink.c b/gst/multifile/gstsplitmuxsink.c
index 260e8e3c4a..0568c657d2 100644
--- a/gst/multifile/gstsplitmuxsink.c
+++ b/gst/multifile/gstsplitmuxsink.c
@@ -338,7 +338,8 @@ gst_splitmux_sink_class_init (GstSplitMuxSinkClass * klass)
           "reserved-duration-remaining properties and use them if so. "
           "(Only present on qtmux and mp4mux for now). splitmuxsink may then also "
           " create new fragments if the reserved header space is about to overflow. "
-          "Note this does not set reserved-moov-update-period - apps should do that manually",
+          "Note that for mp4mux and qtmux, reserved-moov-update-period must be set "
+          "manually by the app to a non-zero value for robust muxing to have an effect.",
           DEFAULT_USE_ROBUST_MUXING,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));