diff --git a/openlp/core/ui/icons.py b/openlp/core/ui/icons.py
index ecfbd9c5a..203bfe705 100644
--- a/openlp/core/ui/icons.py
+++ b/openlp/core/ui/icons.py
@@ -49,9 +49,9 @@ class UiIcons(metaclass=Singleton):
         qta.load_font('op', font_path, charmap_path)
         palette = QtWidgets.QApplication.palette()
         qta.set_defaults(color=palette.color(QtGui.QPalette.Active,
-                                             QtGui.QPalette.ButtonText),
+                                             QtGui.QPalette.WindowText),
                          color_disabled=palette.color(QtGui.QPalette.Disabled,
-                                                      QtGui.QPalette.ButtonText))
+                                                      QtGui.QPalette.WindowText))
         icon_list = {
             'active': {'icon': 'fa.child'},
             'add': {'icon': 'fa.plus-circle'},
diff --git a/tests/functional/openlp_core/lib/test_ui.py b/tests/functional/openlp_core/lib/test_ui.py
index cbcc1b7a0..4312f2b26 100644
--- a/tests/functional/openlp_core/lib/test_ui.py
+++ b/tests/functional/openlp_core/lib/test_ui.py
@@ -88,6 +88,22 @@ def test_critical_error_message_box(MockRegistry):
     MockRegistry.return_value.get.return_value.error_message.assert_called_once_with('Error', 'This is an error')
 
 
+@patch('openlp.core.lib.ui.Registry')
+@patch('openlp.core.lib.ui.QtWidgets.QMessageBox.critical')
+def test_critical_error_message_box_without_mainwindow(mocked_critical, MockRegistry):
+    """
+    Test the critical_error_message_box() function
+    """
+    # GIVEN: A mocked Registry with no MainWindow
+    MockRegistry.return_value.get.return_value = None
+
+    # WHEN: critical_error_message_box() is called
+    critical_error_message_box('Error', 'This is an error')
+
+    # THEN: The error_message() method on the main window should be called
+    mocked_critical.assert_called_once_with(None, 'Error', 'This is an error')
+
+
 @patch('openlp.core.lib.ui.QtWidgets.QMessageBox.critical')
 def test_critical_error_question(mocked_critical):
     """
diff --git a/tests/openlp_core/projectors/test_projector_commands_01.py b/tests/openlp_core/projectors/test_projector_commands_01.py
index b0bb93952..08d036b80 100644
--- a/tests/openlp_core/projectors/test_projector_commands_01.py
+++ b/tests/openlp_core/projectors/test_projector_commands_01.py
@@ -28,6 +28,22 @@ from openlp.core.projectors.pjlinkcommands import process_command
 from openlp.core.projectors.constants import E_ERROR, E_WARN, PJLINK_ERST_DATA, PJLINK_ERST_STATUS, S_OK
 
 
+@patch.object(openlp.core.projectors.pjlinkcommands, 'log')
+def test_projector_ackn(mock_log, pjlink):
+    """
+    Test ackn command (empty test)
+    """
+    # GIVEN: Test setup
+    log_debug_text = [call('({ip}) Processing command "ACKN" with data "0"'.format(ip=pjlink.name)),
+                      call('({ip}) Calling function for ACKN'.format(ip=pjlink.name))]
+
+    # WHEN: Called with setting shutter closed and mute on
+    process_command(projector=pjlink, cmd='ACKN', data='0')
+
+    # THEN: Shutter should be closed and mute should be True
+    mock_log.debug.assert_has_calls(log_debug_text)
+
+
 @patch.object(openlp.core.projectors.pjlink.PJLink, 'projectorUpdateIcons')
 @patch.object(openlp.core.projectors.pjlinkcommands, 'log')
 def test_projector_avmt_audio_muted(mock_log, mock_UpdateIcons, pjlink):