diff --git a/subprojects/gst-plugins-base/docs/plugins/gst_plugins_cache.json b/subprojects/gst-plugins-base/docs/plugins/gst_plugins_cache.json
index 300aa08915..ca9963f1b7 100644
--- a/subprojects/gst-plugins-base/docs/plugins/gst_plugins_cache.json
+++ b/subprojects/gst-plugins-base/docs/plugins/gst_plugins_cache.json
@@ -866,7 +866,7 @@
                         "writable": true
                     },
                     "mix-matrix": {
-                        "blurb": "Transformation matrix for input/output channels",
+                        "blurb": "Transformation matrix for input/output channels.",
                         "conditionally-available": false,
                         "construct": false,
                         "construct-only": false,
diff --git a/subprojects/gst-plugins-base/gst/audioconvert/gstaudioconvert.c b/subprojects/gst-plugins-base/gst/audioconvert/gstaudioconvert.c
index 474dcaea8f..10027bda8b 100644
--- a/subprojects/gst-plugins-base/gst/audioconvert/gstaudioconvert.c
+++ b/subprojects/gst-plugins-base/gst/audioconvert/gstaudioconvert.c
@@ -46,6 +46,9 @@
  *
  * A mix matrix can be passed to audioconvert, that will govern the
  * remapping of input to output channels.
+ * This is required if the input channels are unpositioned and no standard layout can be determined.
+ * If an empty mix matrix is specified, a (potentially truncated) identity matrix will be generated.
+ *
  * ## Example matrix generation code
  * To generate the matrix using code:
  *
@@ -73,8 +76,6 @@
  * gst-launch-1.0 audiotestsrc ! audio/x-raw, channels=4 ! audioconvert mix-matrix="<<(float)1.0, (float)0.0, (float)0.0, (float)0.0>, <(float)0.0, (float)1.0, (float)0.0, (float)0.0>>" ! audio/x-raw,channels=2 ! autoaudiosink
  * ]|
  *
- * > If an empty mix matrix is specified, a (potentially truncated)
- * > identity matrix will be generated.
  *
  * ## Example empty matrix generation code
  * |[
@@ -214,10 +215,18 @@ gst_audio_convert_class_init (GstAudioConvertClass * klass)
           GST_TYPE_AUDIO_NOISE_SHAPING_METHOD, GST_AUDIO_NOISE_SHAPING_NONE,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GstAudioConvert:mix-matrix:
+   *
+   * Transformation matrix for input/output channels.
+   * Required if the input channels are unpositioned and no standard layout can be determined.
+   * Setting an empty matrix like \"< >\" will generate an identity matrix."
+   *
+   */
   g_object_class_install_property (gobject_class, PROP_MIX_MATRIX,
       gst_param_spec_array ("mix-matrix",
           "Input/output channel matrix",
-          "Transformation matrix for input/output channels",
+          "Transformation matrix for input/output channels.",
           gst_param_spec_array ("matrix-rows", "rows", "rows",
               g_param_spec_float ("matrix-cols", "cols", "cols",
                   -1, 1, 0,
@@ -345,8 +354,9 @@ remove_channels_from_structure (GstCapsFeatures * features, GstStructure * s,
   gint channels;
   GstAudioConvert *this = GST_AUDIO_CONVERT (user_data);
 
-  /* Only remove the channels and channel-mask for non-NONE layouts,
-   * or if a mix matrix was manually specified */
+  /* Only remove the channels and channel-mask if a (empty) mix matrix was manually specified,
+   * if no channel-mask is specified, for non-NONE channel layouts or for a single channel layout
+   */
   if (this->mix_matrix_is_set ||
       !gst_structure_get (s, "channel-mask", GST_TYPE_BITMASK, &mask, NULL) ||
       (mask != 0 || (gst_structure_get_int (s, "channels", &channels)
@@ -1006,7 +1016,7 @@ gst_audio_convert_set_property (GObject * object, guint prop_id,
       break;
     case PROP_MIX_MATRIX:
       if (!gst_value_array_get_size (value)) {
-        this->mix_matrix_is_set = FALSE;
+        this->mix_matrix_is_set = TRUE;
       } else {
         const GValue *first_row = gst_value_array_get_value (value, 0);
 
@@ -1017,7 +1027,8 @@ gst_audio_convert_set_property (GObject * object, guint prop_id,
           /* issue a reconfigure upstream */
           gst_base_transform_reconfigure_sink (GST_BASE_TRANSFORM (this));
         } else {
-          g_warning ("Empty mix matrix's first row");
+          g_warning ("Empty mix matrix's first row.");
+          this->mix_matrix_is_set = FALSE;
         }
       }
       break;
diff --git a/subprojects/gst-plugins-base/tests/check/elements/audioconvert.c b/subprojects/gst-plugins-base/tests/check/elements/audioconvert.c
index 7186baf35a..c628caf4d4 100644
--- a/subprojects/gst-plugins-base/tests/check/elements/audioconvert.c
+++ b/subprojects/gst-plugins-base/tests/check/elements/audioconvert.c
@@ -46,7 +46,8 @@ static GstPad *mysrcpad, *mysinkpad;
 
 /* takes over reference for outcaps */
 static GstElement *
-setup_audioconvert (GstCaps * outcaps)
+setup_audioconvert (GstCaps * outcaps, gboolean use_mix_matrix,
+    GValue * mix_matrix)
 {
   GstPadTemplate *sinktemplate;
   static GstStaticPadTemplate srctemplate = GST_STATIC_PAD_TEMPLATE ("src",
@@ -63,6 +64,9 @@ setup_audioconvert (GstCaps * outcaps)
   audioconvert = gst_check_setup_element ("audioconvert");
   g_object_set (G_OBJECT (audioconvert), "dithering", 0, NULL);
   g_object_set (G_OBJECT (audioconvert), "noise-shaping", 0, NULL);
+  if (use_mix_matrix) {
+    g_object_set_property (G_OBJECT (audioconvert), "mix-matrix", mix_matrix);
+  }
   mysrcpad = gst_check_setup_src_pad (audioconvert, &srctemplate);
   mysinkpad =
       gst_check_setup_sink_pad_from_template (audioconvert, sinktemplate);
@@ -408,7 +412,8 @@ get_int_mc_caps (guint channels, gint endianness, guint width,
 static void
 verify_convert (const gchar * which, void *in, int inlength,
     GstCaps * incaps, void *out, int outlength, GstCaps * outcaps,
-    GstFlowReturn expected_flow, gboolean in_place_allowed)
+    GstFlowReturn expected_flow, gboolean in_place_allowed,
+    gboolean use_mix_matrix, GValue * mix_matrix)
 {
   GstBuffer *inbuffer, *outbuffer;
   GstElement *audioconvert;
@@ -419,7 +424,7 @@ verify_convert (const gchar * which, void *in, int inlength,
   GST_DEBUG ("outcaps: %" GST_PTR_FORMAT, outcaps);
   ASSERT_CAPS_REFCOUNT (incaps, "incaps", 1);
   ASSERT_CAPS_REFCOUNT (outcaps, "outcaps", 1);
-  audioconvert = setup_audioconvert (outcaps);
+  audioconvert = setup_audioconvert (outcaps, use_mix_matrix, mix_matrix);
   ASSERT_CAPS_REFCOUNT (outcaps, "outcaps", 2);
 
   fail_unless (gst_element_set_state (audioconvert,
@@ -505,17 +510,22 @@ done:
 #define RUN_CONVERSION(which, inarray, in_get_caps, outarray, out_get_caps)    \
   verify_convert (which, inarray, sizeof (inarray),                            \
         in_get_caps, outarray, sizeof (outarray), out_get_caps, GST_FLOW_OK,   \
-        TRUE)
+        TRUE, FALSE, &(GValue) G_VALUE_INIT);
+
+#define RUN_CONVERSION_WITH_MATRIX(which, inarray, in_get_caps, outarray, out_get_caps, mix_matrix)    \
+  verify_convert (which, inarray, sizeof (inarray),                            \
+        in_get_caps, outarray, sizeof (outarray), out_get_caps, GST_FLOW_OK,   \
+        TRUE, TRUE, mix_matrix);
 
 #define RUN_CONVERSION_TO_FAIL(which, inarray, in_caps, outarray, out_caps)    \
   verify_convert (which, inarray, sizeof (inarray),                            \
         in_caps, outarray, sizeof (outarray), out_caps,                        \
-        GST_FLOW_NOT_NEGOTIATED, TRUE)
+        GST_FLOW_NOT_NEGOTIATED, TRUE, FALSE, &(GValue) G_VALUE_INIT);
 
 #define RUN_CONVERSION_NOT_INPLACE(which, inarray, in_get_caps, outarray, out_get_caps)    \
   verify_convert (which, inarray, sizeof (inarray),                            \
         in_get_caps, outarray, sizeof (outarray), out_get_caps, GST_FLOW_OK,   \
-        FALSE)
+        FALSE, FALSE, &(GValue) G_VALUE_INIT);
 
 #define INTERLEAVED GST_AUDIO_LAYOUT_INTERLEAVED
 #define PLANAR GST_AUDIO_LAYOUT_NON_INTERLEAVED
@@ -1559,6 +1569,53 @@ GST_START_TEST (test_convert_undefined_multichannel)
     RUN_CONVERSION ("8 channels with layout => 2 channels",
         in, in_caps, out, out_caps);
   }
+
+  /* 9 channels, NONE positions => 2 channels, with empty mix-matrix */
+  {
+    guint16 in[] =
+        { 0, 0, 0x8000, 0x8000, 0x8000, 0x8000, 0x8000, 0x8000, 0x8000 };
+    gfloat out[] = { -1.0, -1.0 };
+    GstCaps *in_caps = get_int_mc_caps (9, G_BYTE_ORDER, 16, 16, FALSE,
+        INTERLEAVED, undefined_positions[9 - 1]);
+    GstCaps *out_caps = get_float_mc_caps (2, G_BYTE_ORDER, 32, INTERLEAVED,
+        NULL);
+    GValue empty_mix_matrix = G_VALUE_INIT;
+    g_value_init (&empty_mix_matrix, GST_TYPE_ARRAY);
+
+    RUN_CONVERSION_WITH_MATRIX ("9 channels, undefined layout => 2 channels",
+        in, in_caps, out, out_caps, &empty_mix_matrix);
+    g_value_unset (&empty_mix_matrix);
+  }
+
+  /* 9 channels, NONE positions => 2 channels, with specified mix-matrix */
+  {
+    guint16 in[] =
+        { 0, 0, 0x8000, 0x8000, 0x8000, 0x8000, 0x8000, 0x8000, 0x8000 };
+    gfloat out[] = { -1.0, -1.0 };
+    GstCaps *in_caps = get_int_mc_caps (9, G_BYTE_ORDER, 16, 16, FALSE,
+        INTERLEAVED, undefined_positions[9 - 1]);
+    GstCaps *out_caps = get_float_mc_caps (2, G_BYTE_ORDER, 32, INTERLEAVED,
+        NULL);
+    GValue mix_matrix = G_VALUE_INIT;
+    GValue row = G_VALUE_INIT;
+    GValue value = G_VALUE_INIT;
+    g_value_init (&mix_matrix, GST_TYPE_ARRAY);
+    for (int j = 0; j < 2; j++) {
+      g_value_init (&row, GST_TYPE_ARRAY);
+      for (int i = 0; i < 9; i++) {
+        g_value_init (&value, G_TYPE_FLOAT);
+        g_value_set_float (&value, i == j && i < 2 ? 1 : 0);
+        gst_value_array_append_value (&row, &value);
+        g_value_unset (&value);
+      }
+      gst_value_array_append_value (&mix_matrix, &row);
+      g_value_unset (&row);
+    }
+
+    RUN_CONVERSION_WITH_MATRIX ("9 channels, undefined layout => 2 channels",
+        in, in_caps, out, out_caps, &mix_matrix);
+    g_value_unset (&mix_matrix);
+  }
 }
 
 GST_END_TEST;
@@ -1637,7 +1694,7 @@ GST_START_TEST (test_gap_buffers)
   gsize data_len = sizeof (data);
   gint i;
 
-  audioconvert = setup_audioconvert (caps);
+  audioconvert = setup_audioconvert (caps, FALSE, &(GValue) G_VALUE_INIT);
 
   fail_unless (gst_element_set_state (audioconvert,
           GST_STATE_PLAYING) == GST_STATE_CHANGE_SUCCESS,
@@ -1797,7 +1854,7 @@ GST_START_TEST (test_layout_conv_fixate_caps)
       "layout = (string) non-interleaved, "
       "rate = (int) [ 1, MAX ], " "channels = (int) [1, 8]");
 
-  audioconvert = setup_audioconvert (outcaps);
+  audioconvert = setup_audioconvert (outcaps, FALSE, &(GValue) G_VALUE_INIT);
 
   fail_unless (gst_element_set_state (audioconvert,
           GST_STATE_PLAYING) == GST_STATE_CHANGE_SUCCESS,