Index: src/org/openstreetmap/josm/tools/Geometry.java
===================================================================
--- src/org/openstreetmap/josm/tools/Geometry.java	(revision 19445)
+++ src/org/openstreetmap/josm/tools/Geometry.java	(working copy)
@@ -1562,8 +1562,8 @@
         Pair<Node, Node> closestNodes = null;
         for (Pair<Node, Node> nodes : way.getNodePairs(false)) {
             Way tWay = new Way();
-            tWay.addNode(nodes.a);
-            tWay.addNode(nodes.b);
+            tWay.addNode(new Node(nodes.a));
+            tWay.addNode(new Node(nodes.b));
             double distance = getDistance(tWay, primitive);
             if (distance < lowestDistance) {
                 lowestDistance = distance;
Index: test/unit/org/openstreetmap/josm/tools/GeometryTest.java
===================================================================
--- test/unit/org/openstreetmap/josm/tools/GeometryTest.java	(revision 19445)
+++ test/unit/org/openstreetmap/josm/tools/GeometryTest.java	(working copy)
@@ -36,6 +36,7 @@
 import org.openstreetmap.josm.data.osm.Relation;
 import org.openstreetmap.josm.data.osm.RelationMember;
 import org.openstreetmap.josm.data.osm.Way;
+import org.openstreetmap.josm.data.osm.WaySegment;
 import org.openstreetmap.josm.data.osm.search.SearchCompiler;
 import org.openstreetmap.josm.data.projection.Projection;
 import org.openstreetmap.josm.data.projection.ProjectionRegistry;
@@ -635,4 +636,28 @@
                 () -> Geometry.getCentroid(Arrays.asList(new Node(LatLon.ZERO), new Node(), new Node(LatLon.ZERO))));
         assertTrue(new EastNorth(0, 0).equalsEpsilon(centroid3, 1e-9));
     }
+
+    /**
+     * A non-regression test for an issue found in #24485
+     * Test of {@link Geometry#getClosestWaySegment} method when DataSet is read-only.
+     */
+    @Test
+    void testNonRegression24485() {
+        Node node1 = new Node(new LatLon(0, 0));
+        Node node2 = new Node(new LatLon(0, 1));
+        Node node3 = new Node(new LatLon(0.3, 0.5));
+        Node node4 = new Node(new LatLon(0.1, 0));
+        Way way1 = TestUtils.newWay("", node1, node2, node3, node4);
+
+        DataSet ds = new DataSet();
+        way1.getNodes().forEach(n -> ds.addPrimitive(n));
+        ds.addPrimitive(way1);
+        ds.lock();
+        WaySegment closestSegment = Geometry.getClosestWaySegment(way1, new Node(new LatLon(0, 0.5)));
+        ds.unlock();
+        Way closestSegmentWay = closestSegment.toWay();
+        assertTrue(closestSegmentWay.containsNode(node1));
+        assertTrue(closestSegmentWay.containsNode(node2));
+    }
+
 }