diff --git a/sources/undocommand/mirrorselectioncommand.cpp b/sources/undocommand/mirrorselectioncommand.cpp
index 46dd64078..0f32b0f44 100644
--- a/sources/undocommand/mirrorselectioncommand.cpp
+++ b/sources/undocommand/mirrorselectioncommand.cpp
@@ -83,15 +83,17 @@ MirrorSelectionCommand::MirrorSelectionCommand(const QList<Element *> &elements,
 
 			//The mirror is about the element's hotspot, which is often a
 			//corner of the symbol: move it so that it stays where it was,
-			//centre on centre, and on the grid
+			//centre on centre. The move is snapped to the grid, not the new
+			//position: an element on the grid stays on it, one off the grid
+			//keeps its offset, and a second mirror moves it exactly back.
 		QPointF centre = element->boundingRect().center();
 		centre = QTransform::fromScale(new_horizontal ? -1 : 1, new_vertical ? -1 : 1)
 				 .map(centre);
 		centre = QTransform().rotate(element->rotation()).map(centre);
 
 		const QPointF old_pos = element->pos();
-		const QPointF new_pos = Diagram::snapToGrid(
-					element->mapToScene(element->boundingRect().center()) - centre);
+		const QPointF new_pos = old_pos + Diagram::snapToGrid(
+					element->mapToScene(element->boundingRect().center()) - centre - old_pos);
 		if (new_pos != old_pos)
 			new QPropertyUndoCommand(element, "pos", old_pos, new_pos, this);
 	}
diff --git a/tests/qttest/tst_scriptmirror.cpp b/tests/qttest/tst_scriptmirror.cpp
index 338b5e19d..a75d10aa2 100644
--- a/tests/qttest/tst_scriptmirror.cpp
+++ b/tests/qttest/tst_scriptmirror.cpp
@@ -191,6 +191,48 @@ private slots:
 				 r.value(QStringLiteral("v")).toArray());
 	}
 
+	/**
+		Mirroring a symbol twice the same way puts it back where it was,
+		for every symbol of the project, including those that do not sit
+		on the grid. Before, the second mirror snapped such a symbol onto
+		the grid, a few pixels away. Which symbol mirrorBackAndSave()
+		picks changes from run to run, so this checks them all.
+	*/
+	void mirrorTwiceComesBack_data()
+	{
+		QTest::addColumn<bool>("vertical");
+		QTest::newRow("horizontal") << false;
+		QTest::newRow("vertical")   << true;
+	}
+
+	void mirrorTwiceComesBack()
+	{
+		QFETCH(bool, vertical);
+		const QJsonObject r = run(script(QStringLiteral(
+			"var out = {count: 0, moved: []};\n"
+			"for (var f = 0; f < qet.folioCount(); f++) {\n"
+			"  var els = qet.elementUuids(f);\n"
+			"  for (var e = 0; e < els.length; e++) {\n"
+			"    var before = JSON.stringify(terms(f, els[e]));\n"
+			"    qet.mirrorElement(f, els[e], %1);\n"
+			"    qet.mirrorElement(f, els[e], %1);\n"
+			"    var after = JSON.stringify(terms(f, els[e]));\n"
+			"    out.count++;\n"
+			"    if (after !== before) out.moved.push(els[e] + ' ' + before + ' -> ' + after);\n"
+			"  }\n"
+			"}\n"
+			"qet.log('PROBE ' + JSON.stringify(out));\n")
+			.arg(vertical ? QStringLiteral("true") : QStringLiteral("false"))),
+			QStringLiteral(QET_EXAMPLES_DIR "/perceuse.qet"));
+
+		QVERIFY2(!r.isEmpty(), "the script logged nothing");
+		QVERIFY(r.value(QStringLiteral("count")).toInt() > 0);
+		const QJsonArray moved = r.value(QStringLiteral("moved")).toArray();
+		for (const QJsonValue &m : moved)
+			qWarning("moved: %s", qPrintable(m.toString()));
+		QCOMPARE(moved.size(), 0);
+	}
+
 	/**
 		On a turned symbol a mirror of the folio is the other mirror of the
 		symbol itself, and its rotation does not change: a label kept