diff --git a/run_tests.py b/run_tests.py
index cedf071b..b9687aa9 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -18,6 +18,7 @@ if __name__ == "__main__":
     args = parser.parse_args()
 
     env = os.environ.copy()
+    env["QT_SCALE_FACTOR"] = "1.0"
     cmd = [sys.executable, "-m", "pytest", "-vv"]
 
     if args.o:
diff --git a/tests/test_gui/test_gui_theme.py b/tests/test_gui/test_gui_theme.py
index 68b75fd4..aa2af3cf 100644
--- a/tests/test_gui/test_gui_theme.py
+++ b/tests/test_gui/test_gui_theme.py
@@ -431,11 +431,13 @@ def testGuiTheme_LoadIcons():
     assert qIcon.isNull() is False
 
     # Load it as a pixmap with a size
+    # If this part of the test fails, you may need to set the
+    # environment variable: QT_SCALE_FACTOR=1
     qPix = iconCache.getPixmap("add", (50, 50))
     assert isinstance(qPix, QPixmap)
     assert qPix.isNull() is False
-    assert qPix.width() == 50
-    assert qPix.height() == 50
+    assert qPix.width() == 50, "If this fails, make sure QT_SCALE_FACTOR=1"
+    assert qPix.height() == 50, "If this fails, make sure QT_SCALE_FACTOR=1"
 
     # Load app icon
     qIcon = iconCache.getIcon("novelwriter")