diff --git a/src/backends/meta-monitor-manager.c b/src/backends/meta-monitor-manager.c
index 099a48e74..1cccebc1a 100644
--- a/src/backends/meta-monitor-manager.c
+++ b/src/backends/meta-monitor-manager.c
@@ -1492,7 +1492,7 @@ meta_monitor_manager_legacy_handle_apply_configuration  (MetaDBusDisplayConfig *
 #define META_DISPLAY_CONFIG_MODE_FLAGS_PREFERRED (1 << 0)
 #define META_DISPLAY_CONFIG_MODE_FLAGS_CURRENT (1 << 1)
 
-#define MODE_FORMAT "(iiddadu)"
+#define MODE_FORMAT "(siiddadu)"
 #define MODES_FORMAT "a" MODE_FORMAT
 #define MONITOR_SPEC_FORMAT "(ssss)"
 #define MONITOR_FORMAT "(" MONITOR_SPEC_FORMAT MODES_FORMAT "a{sv})"
@@ -1549,13 +1549,19 @@ meta_monitor_manager_handle_get_current_state (MetaDBusDisplayConfig *skeleton,
         {
           MetaMonitorMode *monitor_mode = k->data;
           GVariantBuilder supported_scales_builder;
-          MetaMonitorModeSpec *monitor_mode_spec;
+          const char *mode_id;
+          int mode_width, mode_height;
+          float refresh_rate;
           float preferred_scale;
           float *supported_scales;
           int n_supported_scales;
           uint32_t flags = 0;
 
-          monitor_mode_spec = meta_monitor_mode_get_spec (monitor_mode);
+          mode_id = meta_monitor_mode_get_id (monitor_mode);
+          meta_monitor_mode_get_resolution (monitor_mode,
+                                            &mode_width, &mode_height);
+          refresh_rate = meta_monitor_mode_get_refresh_rate (monitor_mode);
+
           preferred_scale =
             meta_monitor_manager_calculate_monitor_mode_scale (manager,
                                                                monitor,
@@ -1580,9 +1586,10 @@ meta_monitor_manager_handle_get_current_state (MetaDBusDisplayConfig *skeleton,
             flags |= META_DISPLAY_CONFIG_MODE_FLAGS_PREFERRED;
 
           g_variant_builder_add (&modes_builder, MODE_FORMAT,
-                                 monitor_mode_spec->width,
-                                 monitor_mode_spec->height,
-                                 monitor_mode_spec->refresh_rate,
+                                 mode_id,
+                                 mode_width,
+                                 mode_height,
+                                 refresh_rate,
                                  (double) preferred_scale,
                                  &supported_scales_builder,
                                  flags);
@@ -1797,13 +1804,16 @@ meta_monitor_manager_is_config_applicable (MetaMonitorManager *manager,
   return TRUE;
 }
 
-static MetaMonitorSpec *
-find_monitor_spec (MetaMonitorManager *manager,
-                   char               *connector)
+static MetaMonitor *
+find_monitor_from_connector (MetaMonitorManager *manager,
+                             char               *connector)
 {
   GList *monitors;
   GList *l;
 
+  if (!connector)
+    return NULL;
+
   monitors = meta_monitor_manager_get_monitors (manager);
   for (l = monitors; l; l = l->next)
     {
@@ -1811,14 +1821,13 @@ find_monitor_spec (MetaMonitorManager *manager,
       MetaMonitorSpec *monitor_spec = meta_monitor_get_spec (monitor);
 
       if (g_str_equal (connector, monitor_spec->connector))
-        return meta_monitor_spec_clone (monitor_spec);
+        return monitor;
     }
 
   return NULL;
 }
 
-#define MONITOR_MODE_SPEC_FORMAT "(iid)"
-#define MONITOR_CONFIG_FORMAT "(s" MONITOR_MODE_SPEC_FORMAT "a{sv})"
+#define MONITOR_CONFIG_FORMAT "(ssa{sv})"
 #define MONITOR_CONFIGS_FORMAT "a" MONITOR_CONFIG_FORMAT
 
 #define LOGICAL_MONITOR_CONFIG_FORMAT "(iidub" MONITOR_CONFIGS_FORMAT ")"
@@ -1830,49 +1839,43 @@ create_monitor_config_from_variant (MetaMonitorManager *manager,
 {
 
   MetaMonitorConfig *monitor_config = NULL;
-  char *connector;
+  g_autofree char *connector = NULL;
+  g_autofree char *mode_id = NULL;
+  MetaMonitorMode *monitor_mode;
+  MetaMonitor *monitor;
   MetaMonitorSpec *monitor_spec;
   MetaMonitorModeSpec *monitor_mode_spec;
-  GVariant *properties_variant = NULL;
+  g_autoptr (GVariant) properties_variant = NULL;
   gboolean enable_underscanning = FALSE;
-  int32_t mode_width;
-  int32_t mode_height;
-  double mode_refresh_rate;
 
-  monitor_spec = g_new0 (MetaMonitorSpec, 1);
-  monitor_mode_spec = g_new0 (MetaMonitorModeSpec, 1);
-
-  g_variant_get (monitor_config_variant, "(s" MONITOR_MODE_SPEC_FORMAT "@a{sv})",
+  g_variant_get (monitor_config_variant, "(ss@a{sv})",
                  &connector,
-                 &mode_width,
-                 &mode_height,
-                 &mode_refresh_rate,
+                 &mode_id,
                  &properties_variant);
 
-  *monitor_mode_spec = (MetaMonitorModeSpec) {
-    .width = mode_width,
-    .height = mode_height,
-    .refresh_rate = mode_refresh_rate
-  };
-
-  monitor_spec = find_monitor_spec (manager, connector);
-  if (!monitor_spec)
+  monitor = find_monitor_from_connector (manager, connector);
+  if (!monitor)
     {
       g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                    "Invalid connector '%s' specified", connector);
-      g_free (monitor_mode_spec);
       return NULL;
     }
 
-  if (!meta_verify_monitor_mode_spec (monitor_mode_spec, error))
+  monitor_mode = meta_monitor_get_mode_from_id (monitor, mode_id);
+  if (!monitor_mode)
     {
-      g_free (monitor_mode_spec);
-      meta_monitor_spec_free (monitor_spec);
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Invalid mode '%s' specified", mode_id);
       return NULL;
     }
 
   g_variant_lookup (properties_variant, "underscanning", "b", &enable_underscanning);
 
+  monitor_spec = meta_monitor_spec_clone (meta_monitor_get_spec (monitor));
+
+  monitor_mode_spec = g_new0 (MetaMonitorModeSpec, 1);
+  *monitor_mode_spec = *meta_monitor_mode_get_spec (monitor_mode);
+
   monitor_config = g_new0 (MetaMonitorConfig, 1);
   *monitor_config = (MetaMonitorConfig) {
     .monitor_spec = monitor_spec,
diff --git a/src/backends/meta-monitor.c b/src/backends/meta-monitor.c
index d86cea174..ba12a1341 100644
--- a/src/backends/meta-monitor.c
+++ b/src/backends/meta-monitor.c
@@ -33,6 +33,7 @@
 
 typedef struct _MetaMonitorMode
 {
+  char *id;
   MetaMonitorModeSpec spec;
   MetaMonitorCrtcMode *crtc_modes;
 } MetaMonitorMode;
@@ -50,6 +51,7 @@ typedef struct _MetaMonitorPrivate
 
   GList *outputs;
   GList *modes;
+  GHashTable *mode_ids;
 
   MetaMonitorMode *preferred_mode;
   MetaMonitorMode *current_mode;
@@ -333,6 +335,7 @@ meta_monitor_finalize (GObject *object)
   MetaMonitor *monitor = META_MONITOR (object);
   MetaMonitorPrivate *priv = meta_monitor_get_instance_private (monitor);
 
+  g_hash_table_destroy (priv->mode_ids);
   g_list_free_full (priv->modes, (GDestroyNotify) meta_monitor_mode_free);
   g_clear_pointer (&priv->outputs, g_list_free);
   meta_monitor_spec_free (priv->spec);
@@ -341,6 +344,9 @@ meta_monitor_finalize (GObject *object)
 static void
 meta_monitor_init (MetaMonitor *monitor)
 {
+  MetaMonitorPrivate *priv = meta_monitor_get_instance_private (monitor);
+
+  priv->mode_ids = g_hash_table_new (g_str_hash, g_str_equal);
 }
 
 static void
@@ -351,6 +357,36 @@ meta_monitor_class_init (MetaMonitorClass *klass)
   object_class->finalize = meta_monitor_finalize;
 }
 
+static char *
+generate_mode_id (MetaMonitorModeSpec *monitor_mode_spec)
+{
+  char refresh_rate_str[G_ASCII_DTOSTR_BUF_SIZE];
+
+  g_ascii_dtostr (refresh_rate_str, G_ASCII_DTOSTR_BUF_SIZE,
+                  monitor_mode_spec->refresh_rate);
+
+  return g_strdup_printf ("%dx%d@%s",
+                          monitor_mode_spec->width,
+                          monitor_mode_spec->height,
+                          refresh_rate_str);
+}
+
+static gboolean
+meta_monitor_add_mode (MetaMonitor     *monitor,
+                       MetaMonitorMode *monitor_mode)
+{
+  MetaMonitorPrivate *priv = meta_monitor_get_instance_private (monitor);
+
+  if (g_hash_table_lookup (priv->mode_ids,
+                           meta_monitor_mode_get_id (monitor_mode)))
+    return FALSE;
+
+  priv->modes = g_list_append (priv->modes, monitor_mode);
+  g_hash_table_insert (priv->mode_ids, monitor_mode->id, monitor_mode);
+
+  return TRUE;
+}
+
 static void
 meta_monitor_normal_generate_modes (MetaMonitorNormal *monitor_normal)
 {
@@ -372,6 +408,7 @@ meta_monitor_normal_generate_modes (MetaMonitorNormal *monitor_normal)
         .height = crtc_mode->height,
         .refresh_rate = crtc_mode->refresh_rate
       },
+      mode->id = generate_mode_id (&mode->spec);
       mode->crtc_modes = g_new (MetaMonitorCrtcMode, 1);
       mode->crtc_modes[0] = (MetaMonitorCrtcMode) {
         .output = output,
@@ -383,7 +420,8 @@ meta_monitor_normal_generate_modes (MetaMonitorNormal *monitor_normal)
       if (output->crtc && crtc_mode == output->crtc->current_mode)
         monitor_priv->current_mode = mode;
 
-      monitor_priv->modes = g_list_append (monitor_priv->modes, mode);
+      if (!meta_monitor_add_mode (monitor, mode))
+        meta_monitor_mode_free (mode);
     }
 }
 
@@ -671,15 +709,22 @@ create_tiled_monitor_mode (MetaMonitorTiled *monitor_tiled,
   MetaMonitorPrivate *monitor_priv =
     meta_monitor_get_instance_private (monitor);
   MetaMonitorModeTiled *mode;
+  int width, height;
   GList *l;
   unsigned int i;
   gboolean is_preferred = TRUE;
 
   mode = g_new0 (MetaMonitorModeTiled, 1);
   mode->is_tiled = TRUE;
-  meta_monitor_tiled_calculate_tiled_size (monitor,
-                                           &mode->parent.spec.width,
-                                           &mode->parent.spec.height);
+  meta_monitor_tiled_calculate_tiled_size (monitor, &width, &height);
+
+  mode->parent.spec = (MetaMonitorModeSpec) {
+    .width = width,
+    .height = height,
+    .refresh_rate = refresh_rate,
+  };
+  mode->parent.id = generate_mode_id (&mode->parent.spec);
+
   mode->parent.crtc_modes = g_new0 (MetaMonitorCrtcMode,
                                     g_list_length (monitor_priv->outputs));
   for (l = monitor_priv->outputs, i = 0; l; l = l->next, i++)
@@ -701,8 +746,6 @@ create_tiled_monitor_mode (MetaMonitorTiled *monitor_tiled,
         .crtc_mode = tiled_crtc_mode
       };
 
-      mode->parent.spec.refresh_rate = refresh_rate;
-
       is_preferred = is_preferred && tiled_crtc_mode == output->preferred_mode;
     }
 
@@ -720,6 +763,8 @@ generate_tiled_monitor_modes (MetaMonitorTiled *monitor_tiled)
   MetaOutput *main_output;
   GList *tiled_modes = NULL;
   unsigned int i;
+  MetaMonitorMode *best_mode = NULL;
+  GList *l;
 
   main_output = meta_monitor_get_main_output (META_MONITOR (monitor_tiled));
 
@@ -746,24 +791,28 @@ generate_tiled_monitor_modes (MetaMonitorTiled *monitor_tiled)
         monitor_priv->preferred_mode = mode;
     }
 
-  if (!monitor_priv->preferred_mode)
+  while ((l = tiled_modes))
     {
-      MetaMonitorMode *best_mode = NULL;
-      GList *l;
+      MetaMonitorMode *mode = l->data;
 
-      for (l = tiled_modes; l; l = l->next)
+      tiled_modes = g_list_remove_link (tiled_modes, l);
+
+      if (!meta_monitor_add_mode (monitor, mode))
         {
-          MetaMonitorMode *mode = l->data;
+          meta_monitor_mode_free (mode);
+          continue;
+        }
 
+      if (!monitor_priv->preferred_mode)
+        {
           if (!best_mode ||
               mode->spec.refresh_rate > best_mode->spec.refresh_rate)
             best_mode = mode;
         }
-
-      monitor_priv->preferred_mode = best_mode;
     }
 
-  monitor_priv->modes = g_list_concat (monitor_priv->modes, tiled_modes);
+  if (best_mode)
+    monitor_priv->preferred_mode = best_mode;
 }
 
 static MetaMonitorMode *
@@ -789,6 +838,7 @@ create_untiled_monitor_mode (MetaMonitorTiled *monitor_tiled,
     .height = crtc_mode->height,
     .refresh_rate = crtc_mode->refresh_rate
   };
+  mode->parent.id = generate_mode_id (&mode->parent.spec);
   mode->parent.crtc_modes = g_new0 (MetaMonitorCrtcMode,
                              g_list_length (monitor_priv->outputs));
 
@@ -888,7 +938,11 @@ generate_untiled_monitor_modes (MetaMonitorTiled *monitor_tiled)
       if (!mode)
         continue;
 
-      monitor_priv->modes = g_list_append (monitor_priv->modes, mode);
+      if (!meta_monitor_add_mode (monitor, mode))
+        {
+          meta_monitor_mode_free (mode);
+          continue;
+        }
 
       if (is_monitor_mode_assigned (monitor, mode))
         {
@@ -1130,6 +1184,7 @@ meta_monitor_tiled_class_init (MetaMonitorTiledClass *klass)
 static void
 meta_monitor_mode_free (MetaMonitorMode *monitor_mode)
 {
+  g_free (monitor_mode->id);
   g_free (monitor_mode->crtc_modes);
   g_free (monitor_mode);
 }
@@ -1153,6 +1208,15 @@ meta_monitor_get_logical_monitor (MetaMonitor *monitor)
     return NULL;
 }
 
+MetaMonitorMode *
+meta_monitor_get_mode_from_id (MetaMonitor *monitor,
+                               const char  *monitor_mode_id)
+{
+  MetaMonitorPrivate *priv = meta_monitor_get_instance_private (monitor);
+
+  return g_hash_table_lookup (priv->mode_ids, monitor_mode_id);
+}
+
 static gboolean
 meta_monitor_mode_spec_equals (MetaMonitorModeSpec *monitor_mode_spec,
                                MetaMonitorModeSpec *other_monitor_mode_spec)
@@ -1458,6 +1522,12 @@ meta_monitor_mode_get_spec (MetaMonitorMode *monitor_mode)
   return &monitor_mode->spec;
 }
 
+const char *
+meta_monitor_mode_get_id (MetaMonitorMode *monitor_mode)
+{
+  return monitor_mode->id;
+}
+
 void
 meta_monitor_mode_get_resolution (MetaMonitorMode *monitor_mode,
                                   int             *width,
diff --git a/src/backends/meta-monitor.h b/src/backends/meta-monitor.h
index 3e40a9de7..73903617f 100644
--- a/src/backends/meta-monitor.h
+++ b/src/backends/meta-monitor.h
@@ -145,6 +145,9 @@ gboolean meta_monitor_get_suggested_position (MetaMonitor *monitor,
 
 MetaLogicalMonitor * meta_monitor_get_logical_monitor (MetaMonitor *monitor);
 
+MetaMonitorMode * meta_monitor_get_mode_from_id (MetaMonitor *monitor,
+                                                 const char  *monitor_mode_id);
+
 MetaMonitorMode * meta_monitor_get_mode_from_spec (MetaMonitor         *monitor,
                                                    MetaMonitorModeSpec *monitor_mode_spec);
 
@@ -174,6 +177,8 @@ float * meta_monitor_calculate_supported_scales (MetaMonitor                *mon
                                                  MetaMonitorScalesConstraint constraints,
                                                  int                        *n_supported_scales);
 
+const char * meta_monitor_mode_get_id (MetaMonitorMode *monitor_mode);
+
 MetaMonitorModeSpec * meta_monitor_mode_get_spec (MetaMonitorMode *monitor_mode);
 
 void meta_monitor_mode_get_resolution (MetaMonitorMode *monitor_mode,
diff --git a/src/org.gnome.Mutter.DisplayConfig.xml b/src/org.gnome.Mutter.DisplayConfig.xml
index 62b82659c..befd68580 100644
--- a/src/org.gnome.Mutter.DisplayConfig.xml
+++ b/src/org.gnome.Mutter.DisplayConfig.xml
@@ -315,7 +315,8 @@
 	* s vendor: vendor name
 	* s product: product name
 	* s serial: product serial
-	* a(iiddadu) modes: available modes
+	* a(siiddad) modes: available modes
+	    * s id: mode ID
 	    * i width: width in physical pixels
 	    * i height: height in physical pixels
 	    * d refresh rate: refresh rate
@@ -404,7 +405,7 @@
     -->
     <method name="GetCurrentState">
       <arg name="serial" direction="out" type="u" />
-      <arg name="monitors" direction="out" type="a((ssss)a(iiddadu)a{sv})" />
+      <arg name="monitors" direction="out" type="a((ssss)a(siiddadu)a{sv})" />
       <arg name="logical_monitors" direction="out" type="a(iiduba(ssss)a{sv})" />
       <arg name="properties" direction="out" type="a{sv}" />
     </method>
@@ -431,10 +432,9 @@
 	* d: scale
 	* u: transform (see GetCurrentState)
 	* b primary: true if this is the primary logical monitor
-	* a(siida{sv}): a list of monitors, each consisting of:
+	* a(ssa{sv}): a list of monitors, each consisting of:
 	    * s: connector
-	    * (iid): monitor mode spec (resolution width, resolution height,
-		     refresh rate)
+	    * s: monitor mode ID
 	    * a{sv}: monitor properties, including:
 	        - "enable_underscanning" (b): enable monitor underscanning;
 					      may only be set when underscanning
@@ -450,7 +450,7 @@
     <method name="ApplyMonitorsConfig">
       <arg name="serial" direction="in" type="u" />
       <arg name="method" direction="in" type="u" />
-      <arg name="logical_monitors" direction="in" type="a(iiduba(s(iid)a{sv}))" />
+      <arg name="logical_monitors" direction="in" type="a(iiduba(ssa{sv}))" />
       <arg name="properties" direction="in" type="a{sv}" />
     </method>
   </interface>