diff --git a/app/qrwebform.py b/app/qrwebform.py
index d48806b..d7bebd6 100755
--- a/app/qrwebform.py
+++ b/app/qrwebform.py
@@ -13,7 +13,11 @@ app.config['SECRET_KEY'] = os.urandom(40)
 
 class QRForm(FlaskForm):
     user_data = TextField("Dane:", validators=[DataRequired()])
-    trim_spaces = BooleanField("Usuń spacje", default=True)
+    # setting default here doesn't work, so we cannot retain checkbox state over POST
+    # we force trim_spaced to be checked in the template
+    # see https://github.com/wtforms/flask-wtf/issues/489 https://github.com/wtforms/flask-wtf/issues/362
+    # https://github.com/wtforms/flask-wtf/issues/464
+    trim_spaces = BooleanField("Usuń spacje")
     submit = SubmitField("Generuj")
 
     @app.route("/", methods=["GET", "POST"])