diff --git a/portal/flatpak-portal.c b/portal/flatpak-portal.c
index 3b230ff4..2fcbd6a9 100644
--- a/portal/flatpak-portal.c
+++ b/portal/flatpak-portal.c
@@ -773,6 +773,7 @@ handle_spawn (PortalFlatpak         *object,
   g_auto(GStrv) runtime_parts = NULL;
   g_autofree char *runtime_commit = NULL;
   g_autofree char *instance_path = NULL;
+  g_autofree char *instance_id = NULL;
   g_auto(GStrv) extra_args = NULL;
   g_auto(GStrv) shares = NULL;
   g_auto(GStrv) sockets = NULL;
@@ -780,6 +781,7 @@ handle_spawn (PortalFlatpak         *object,
   g_auto(GStrv) unset_env = NULL;
   g_auto(GStrv) sandbox_expose = NULL;
   g_auto(GStrv) sandbox_expose_ro = NULL;
+  g_autoptr(FlatpakInstance) instance = NULL;
   g_autoptr(GVariant) sandbox_expose_fd = NULL;
   g_autoptr(GVariant) sandbox_expose_fd_ro = NULL;
   g_autoptr(GVariant) app_fd = NULL;
@@ -988,8 +990,36 @@ handle_spawn (PortalFlatpak         *object,
       max_fd = MAX (max_fd, fd_map_entry.from);
     }
 
-  /* TODO: Ideally we should let `flatpak run` inherit the portal's
-   * environment, in case e.g. a LD_LIBRARY_PATH is needed to be able
+  if (testing)
+    {
+      instance_id = g_strdup ("11223344");
+    }
+  else
+    {
+      instance_id = g_key_file_get_string (app_info,
+                                           FLATPAK_METADATA_GROUP_INSTANCE,
+                                           FLATPAK_METADATA_KEY_INSTANCE_ID, NULL);
+    }
+
+  if (!instance_id)
+    {
+      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                             G_DBUS_ERROR_INVALID_ARGS,
+                                             "Caller has no instance id");
+      return G_DBUS_METHOD_INVOCATION_HANDLED;
+    }
+
+  instance = flatpak_instance_new_for_id (instance_id);
+  if (!instance)
+    {
+      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                             G_DBUS_ERROR_FAILED,
+                                             "Could not access caller instance");
+      return G_DBUS_METHOD_INVOCATION_HANDLED;
+    }
+
+  /* TODO: Ideally we should let `flatpak run` inherit the run environment
+   * of the instance, in case e.g. a LD_LIBRARY_PATH is needed to be able
    * to run `flatpak run`, but tell it to start from a blank environment
    * when running the Flatpak app; but this isn't currently possible, so
    * for now we preserve existing behaviour. */
@@ -999,7 +1029,31 @@ handle_spawn (PortalFlatpak         *object,
       env = g_strdupv (empty);
     }
   else
-    env = g_get_environ ();
+    {
+      static const char * const mock_run_environ[] = { "FOO=bar", NULL };
+
+      if (testing)
+        env = g_strdupv ((GStrv) mock_run_environ);
+      else
+        env = flatpak_instance_get_run_environ (instance, &error);
+
+      if (env == NULL)
+        {
+          if (g_error_matches (error, G_FILE_ERROR, G_FILE_ERROR_NOENT))
+            {
+              g_warning ("Environment for \"flatpak run\" was not found, falling back to current environment");
+              env = g_get_environ ();
+            }
+          else
+            {
+              g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                                     G_DBUS_ERROR_INVALID_ARGS,
+                                                     "Could not load environment for \"flatpak run\": %s",
+                                                     error->message);
+              return G_DBUS_METHOD_INVOCATION_HANDLED;
+            }
+        }
+    }
 
   if ((flatpak = g_getenv ("FLATPAK_PORTAL_MOCK_FLATPAK")) != NULL)
     g_ptr_array_add (flatpak_argv, g_strdup (flatpak));
@@ -1167,7 +1221,6 @@ handle_spawn (PortalFlatpak         *object,
 
   if (expose_pids || share_pids)
     {
-      g_autofree char *instance_id = NULL;
       int sender_pid1 = 0;
 
       if (!(supports & FLATPAK_SPAWN_SUPPORT_FLAGS_EXPOSE_PIDS))
@@ -1178,16 +1231,7 @@ handle_spawn (PortalFlatpak         *object,
           return G_DBUS_METHOD_INVOCATION_HANDLED;
         }
 
-      instance_id = g_key_file_get_string (app_info,
-                                           FLATPAK_METADATA_GROUP_INSTANCE,
-                                           FLATPAK_METADATA_KEY_INSTANCE_ID, NULL);
-
-      if (instance_id)
-        {
-          g_autoptr(FlatpakInstance) instance = flatpak_instance_new_for_id (instance_id);
-          sender_pid1 = flatpak_instance_get_child_pid (instance);
-        }
-
+      sender_pid1 = flatpak_instance_get_child_pid (instance);
       if (sender_pid1 == 0)
         {
           g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,