diff --git a/src/lib/core/SelectionBox.h b/src/lib/core/SelectionBox.h
index 12f2e74..34a57de 100644
--- a/src/lib/core/SelectionBox.h
+++ b/src/lib/core/SelectionBox.h
@@ -15,14 +15,17 @@
 
 // Whether the box overlaps the unit square of `tile` — the rule for anything that
 // occupies whole tiles (buildings, construction sites, defence station bodies). The
-// comparisons are inclusive, so a box that only grazes the tile's edge still covers
-// it, and a box with no area covers the tile it lies on.
+// overlap must have area: a box that ends exactly on a tile boundary does not reach
+// into the tile beyond it. That matters because a click resolves as the unit square
+// of the tile it hit (GameWorldView::getBoxWorldRect), so its edges lie exactly on
+// tile boundaries — with the touching edges counted as coverage, such a box would
+// cover the whole 3x3 neighbourhood instead of the one tile clicked.
 inline bool boxCoversTile(const QRectF& worldBox, QPoint tile)
 {
-    return worldBox.left() <= static_cast<qreal>(tile.x()) + 1.0
-        && worldBox.right() >= static_cast<qreal>(tile.x())
-        && worldBox.top() <= static_cast<qreal>(tile.y()) + 1.0
-        && worldBox.bottom() >= static_cast<qreal>(tile.y());
+    return worldBox.left() < static_cast<qreal>(tile.x()) + 1.0
+        && worldBox.right() > static_cast<qreal>(tile.x())
+        && worldBox.top() < static_cast<qreal>(tile.y()) + 1.0
+        && worldBox.bottom() > static_cast<qreal>(tile.y());
 }
 
 // Whether the box contains `worldPos` — the rule for anything that has a position
diff --git a/src/test/BuildingTest.cpp b/src/test/BuildingTest.cpp
index d64dbcd..357e6b5 100644
--- a/src/test/BuildingTest.cpp
+++ b/src/test/BuildingTest.cpp
@@ -168,6 +168,29 @@ TEST_CASE("buildingsInBox covers a body cell the box only reaches into", "[build
     REQUIRE(buildingsInBox(f.state, QRectF(1.2, 1.2, 0.5, 0.5)).empty());
 }
 
+TEST_CASE("buildingsInBox stops at the edge of a tile-aligned box", "[building]")
+{
+    PlacementFixture f;
+
+    const BuildingId id = f.bs.place(f.state, BuildingType::Miner, QPoint(0, 0),
+                                     Rotation::East, 0).value();
+
+    // Body at (0,0),(1,0),(0,1). A click resolves as the unit square of the tile it
+    // hit (GameWorldView::getBoxWorldRect), so the box edges land exactly on tile
+    // boundaries -- the case where an over-inclusive coverage rule reaches into the
+    // neighbouring tiles (REQ-UI-MULTI-SELECT).
+    const std::vector<BuildingId> onBody =
+        buildingsInBox(f.state, QRectF(1.0, 0.0, 1.0, 1.0));
+    REQUIRE(onBody.size() == 1);
+    REQUIRE(onBody.front() == id);
+
+    // (2,0) is empty and merely touches the body cell (1,0) along their shared edge;
+    // clicking it must select nothing. Same for (1,1), which touches (1,0) and (0,1)
+    // along an edge each and (0,0) at a corner.
+    REQUIRE(buildingsInBox(f.state, QRectF(2.0, 0.0, 1.0, 1.0)).empty());
+    REQUIRE(buildingsInBox(f.state, QRectF(1.0, 1.0, 1.0, 1.0)).empty());
+}
+
 // -- World-bounds rejection (REQ-BLD-PLACE-VALID) ---------------------------
 
 TEST_CASE("BuildingSystem: place rejects a building above the world (y < 0)", "[building]")