diff --git a/sources/autoNum/ui/autonumberingdockwidget.ui b/sources/autoNum/ui/autonumberingdockwidget.ui
index 8fc90c33d..ac0e366c5 100644
--- a/sources/autoNum/ui/autonumberingdockwidget.ui
+++ b/sources/autoNum/ui/autonumberingdockwidget.ui
@@ -92,12 +92,6 @@
     </item>
     <item row="2" column="4">
      <widget class="QSpinBox" name="m_conductor_increase_sb">
-      <property name="maximumSize">
-       <size>
-        <width>55</width>
-        <height>16777215</height>
-       </size>
-      </property>
       <property name="toolTip">
        <string>Increment: the value added to the counter each time a new number is dialled</string>
       </property>
@@ -179,12 +173,6 @@
     </item>
     <item row="3" column="4">
      <widget class="QSpinBox" name="m_element_increase_sb">
-      <property name="maximumSize">
-       <size>
-        <width>55</width>
-        <height>16777215</height>
-       </size>
-      </property>
       <property name="toolTip">
        <string>Increment: the value added to the counter each time a new number is dialled</string>
       </property>
@@ -255,12 +243,6 @@
     </item>
     <item row="4" column="4">
      <widget class="QSpinBox" name="m_folio_increase_sb">
-      <property name="maximumSize">
-       <size>
-        <width>55</width>
-        <height>16777215</height>
-       </size>
-      </property>
       <property name="toolTip">
        <string>Increment: the value added to the counter each time a new number is dialled</string>
       </property>
diff --git a/tests/qttest/CMakeLists.txt b/tests/qttest/CMakeLists.txt
index 496e381ee..ce15d0f30 100644
--- a/tests/qttest/CMakeLists.txt
+++ b/tests/qttest/CMakeLists.txt
@@ -312,6 +312,10 @@ qet_add_app_test(tst_folioimageload tst_folioimageload.cpp)
 # edit (#1566) and gets back the height the user gave it (#1439).
 qet_add_app_test(tst_selectionpanelheight tst_selectionpanelheight.cpp)
 
+# The Auto numbering panel's Increment spin boxes get the width their style
+# asks for; a fixed 55 px cut the number off on Windows (#1566).
+qet_add_app_test(tst_autonumincrementwidth tst_autonumincrementwidth.cpp)
+
 # Opening a project before the elements panel's first reload() left its tree
 # item detached, and selecting the item's first child crashed in QTreeModel
 # (pre-existing since a82f6de23).
diff --git a/tests/qttest/tst_autonumincrementwidth.cpp b/tests/qttest/tst_autonumincrementwidth.cpp
new file mode 100644
index 000000000..23b0f0150
--- /dev/null
+++ b/tests/qttest/tst_autonumincrementwidth.cpp
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "qetapptest.h"
+
+#include <QDockWidget>
+#include <QProxyStyle>
+#include <QSpinBox>
+
+namespace {
+
+// Spin boxes as wide as the Windows 11 style draws them: its up and down
+// buttons sit side by side, so a spin box needs far more room than with
+// the buttons stacked.
+class WideSpinBoxStyle : public QProxyStyle
+{
+	public:
+		QSize sizeFromContents(ContentsType type, const QStyleOption *option,
+				       const QSize &size, const QWidget *widget) const override
+		{
+			QSize s = QProxyStyle::sizeFromContents(type, option, size, widget);
+			if (type == CT_SpinBox)
+				s.rwidth() += 40;
+			return s;
+		}
+};
+
+}
+
+// The Increment spin boxes of the Auto numbering panel get the width their
+// style asks for (#1566). A fixed 55 px maximum cut off the number on
+// Windows.
+class tst_autonumincrementwidth : public QObject
+{
+	Q_OBJECT
+
+	private slots:
+		void incrementFitsItsStyle()
+		{
+			QApplication::setStyle(new WideSpinBoxStyle);
+
+			QETDiagramEditor *editor = QetAppTest::editor();
+			QVERIFY(editor);
+			editor->resize(1600, 1000);
+			editor->show();
+			QVERIFY(QTest::qWaitForWindowExposed(editor));
+
+			const QStringList names{"m_conductor_increase_sb",
+						"m_element_increase_sb",
+						"m_folio_increase_sb"};
+			for (const QString &name : names) {
+				auto spin_box = editor->findChild<QSpinBox *>(name);
+				QVERIFY2(spin_box, qPrintable(name));
+				QVERIFY2(spin_box->isVisible(), qPrintable(name));
+				QVERIFY2(spin_box->width() >= spin_box->minimumSizeHint().width(),
+					 qPrintable(QString("%1 is %2 px, its style needs %3 px")
+						    .arg(name)
+						    .arg(spin_box->width())
+						    .arg(spin_box->minimumSizeHint().width())));
+			}
+		}
+};
+
+QET_APP_TEST_MAIN(tst_autonumincrementwidth)
+
+#include "tst_autonumincrementwidth.moc"