diff --git a/spinetoolbox/ui_main.py b/spinetoolbox/ui_main.py
index e0dd5d114..42eb210c8 100644
--- a/spinetoolbox/ui_main.py
+++ b/spinetoolbox/ui_main.py
@@ -44,6 +44,7 @@
     QMenu,
     QMessageBox,
     QScrollArea,
+    QStyleFactory,
     QToolButton,
     QVBoxLayout,
     QWidget,
@@ -128,6 +129,7 @@ def __init__(self):
         from .ui.mainwindow import Ui_MainWindow  # pylint: disable=import-outside-toplevel
 
         super().__init__(flags=Qt.Window)
+        self.set_app_style()
         self.set_error_mode()
         self._qsettings = QSettings("SpineProject", "Spine Toolbox", self)
         self._update_qsettings()
@@ -315,6 +317,14 @@ def connect_signals(self):
         self.kernel_shutdown.connect(self._handle_kernel_shutdown)
         self.persistent_console_requested.connect(self._setup_persistent_console, Qt.BlockingQueuedConnection)
 
+    @staticmethod
+    def set_app_style():
+        """Sets app style on Windows to 'windowsvista' or to a default if not available."""
+        if sys.platform == "win32":
+            if "windowsvista" not in QStyleFactory.keys():
+                return
+            QApplication.setStyle("windowsvista")
+
     @staticmethod
     def set_error_mode():
         """Sets Windows error mode to show all error dialog boxes from subprocesses.
diff --git a/tests/mock_helpers.py b/tests/mock_helpers.py
index c7c991487..e81edc73b 100644
--- a/tests/mock_helpers.py
+++ b/tests/mock_helpers.py
@@ -22,10 +22,13 @@
 
 def create_toolboxui():
     """Returns ToolboxUI, where QSettings among others has been mocked."""
-    with mock.patch("spinetoolbox.plugin_manager.PluginManager.load_installed_plugins"), mock.patch(
-        "spinetoolbox.ui_main.QSettings.value"
-    ) as mock_qsettings_value:
+    with mock.patch(
+            "spinetoolbox.ui_main.QSettings.value") as mock_qsettings_value, mock.patch(
+        "spinetoolbox.ui_main.ToolboxUI.set_app_style") as mock_set_app_style, mock.patch(
+        "spinetoolbox.plugin_manager.PluginManager.load_installed_plugins"
+    ):
         mock_qsettings_value.side_effect = qsettings_value_side_effect
+        mock_set_app_style.return_value = True
         toolbox = ToolboxUI()
     return toolbox
 
@@ -41,16 +44,15 @@ def create_project(toolbox, project_dir):
 def create_toolboxui_with_project(project_dir):
     """Returns ToolboxUI with a project instance where
     QSettings among others has been mocked."""
-    with mock.patch("spinetoolbox.ui_main.ToolboxUI.save_project"), mock.patch(
-        "spinetoolbox.ui_main.QSettings.value"
-    ) as mock_qsettings_value, mock.patch("spinetoolbox.ui_main.QSettings.setValue"), mock.patch(
-        "spinetoolbox.ui_main.QSettings.sync"
-    ), mock.patch(
-        "spinetoolbox.plugin_manager.PluginManager.load_installed_plugins"
-    ), mock.patch(
-        "spinetoolbox.ui_main.QScrollArea.setWidget"
-    ):
+    with mock.patch("spinetoolbox.ui_main.QSettings.value") as mock_qsettings_value, mock.patch(
+            "spinetoolbox.ui_main.ToolboxUI.set_app_style") as mock_set_app_style, mock.patch(
+            "spinetoolbox.ui_main.ToolboxUI.save_project"), mock.patch(
+            "spinetoolbox.ui_main.QSettings.setValue"), mock.patch(
+            "spinetoolbox.ui_main.QSettings.sync"), mock.patch(
+            "spinetoolbox.plugin_manager.PluginManager.load_installed_plugins"), mock.patch(
+            "spinetoolbox.ui_main.QScrollArea.setWidget"):
         mock_qsettings_value.side_effect = qsettings_value_side_effect
+        mock_set_app_style.return_value = True
         toolbox = ToolboxUI()
         toolbox.create_project(project_dir)
     return toolbox