Index: src/org/openstreetmap/josm/actions/CombineWayAction.java
===================================================================
--- src/org/openstreetmap/josm/actions/CombineWayAction.java	(revision 15607)
+++ src/org/openstreetmap/josm/actions/CombineWayAction.java	(working copy)
@@ -116,7 +116,7 @@
         // remove duplicates, preserving order
         ways = new LinkedHashSet<>(ways);
         // remove incomplete ways
-        ways.removeIf(OsmPrimitive::isIncomplete);
+        ways.removeIf(w -> w.isIncomplete() || w.isOutsideDownloadArea());
         // we need at least two ways
         if (ways.size() < 2)
             return null;
@@ -325,7 +325,8 @@
         int numWays = 0;
         if (OsmUtils.isOsmCollectionEditable(selection)) {
             for (OsmPrimitive osm : selection) {
-                if (osm instanceof Way && !osm.isIncomplete() && ++numWays >= 2) {
+                if (osm instanceof Way && !osm.isIncomplete() && !((Way) osm).isOutsideDownloadArea()
+                        && ++numWays >= 2) {
                     break;
                 }
             }