diff --git a/src/instances/instance.gd b/src/instances/instance.gd
index 0edc293..854749d 100644
--- a/src/instances/instance.gd
+++ b/src/instances/instance.gd
@@ -135,6 +135,8 @@ func _populate() -> void:
 			var at := world.map.tile_centre(tx, ty)
 			if world.map.circle_blocked(at, def.radius):
 				continue
+			if _would_see_the_entrance(def, at):
+				continue
 			world.spawn_enemy(def, at, rng.randi_range(0, 120))
 	# After every room, so adding tunnel groups leaves each room's population
 	# exactly what that seed always produced.
@@ -189,6 +191,25 @@ func _populate_tunnels(rng: RandomNumberGenerator, flavour: DungeonDef) -> void:
 			world.spawn_enemy(member, spots[i], rng.randi_range(0, 120))
 
 
+## Whether an enemy placed at [param at] would be awake the moment the party
+## arrives: within its aggro range of the entrance, with nothing in the way --
+## the same two questions SimWorld._aggro_target asks.
+##
+## Room 0 is left empty for exactly this reason, but that only ever covered room
+## 0. A neighbouring room in sight of the entrance woke on arrival in one run in
+## eight, and once tunnels were widened -- more open ground, more lines of sight
+## -- in three runs in eight. Skipping these removes about one enemy in sixteen;
+## clearing everything within aggro range instead would have removed nearly a
+## third, which is a different dungeon rather than a fixed one.
+##
+## The rng draws for the skipped enemy have already been made, so every other
+## enemy in the dungeon is exactly where that seed always put it.
+func _would_see_the_entrance(def: EnemyDef, at: Vector2) -> bool:
+	if at.distance_to(world.spawn_point) > def.aggro_range:
+		return false
+	return world.map.has_line_of_sight(at, world.spawn_point)
+
+
 ## Floor tiles of [param leg] that are tunnel rather than room: clear of every
 ## room by a tile, so a group is never standing in a doorway, and outside the
 ## boss arena.
diff --git a/tests/integration/test_dungeon_flow.gd b/tests/integration/test_dungeon_flow.gd
index 5db2e8d..4b3c6e9 100644
--- a/tests/integration/test_dungeon_flow.gd
+++ b/tests/integration/test_dungeon_flow.gd
@@ -211,3 +211,26 @@ func test_boss_rush_leaves_the_tunnels_empty_too() -> void:
 	var run := Instance.make_dungeon(2, 4242, 3)
 	GameOpts.boss_rush = false
 	assert_eq(_tunnel_enemies(run).size(), 0)
+
+
+func test_nothing_is_awake_and_watching_when_the_party_arrives() -> void:
+	# Room 0 is left empty so that arriving is not an ambush, but that only ever
+	# covered room 0. With tunnels widened, three runs in eight had an enemy in
+	# a neighbouring room within aggro range and in sight of the entrance.
+	var watching := 0
+	for s in range(1, 120):
+		var run := Instance.make_dungeon(2, s * 7919, 1 + (s % 3))
+		for e in run.world.enemies.values():
+			if e.pos.distance_to(run.world.spawn_point) <= e.def.aggro_range \
+					and run.world.map.has_line_of_sight(e.pos, run.world.spawn_point):
+				watching += 1
+	assert_eq(watching, 0, "%d enemies could see the entrance at the moment of arrival" % watching)
+
+
+func test_clearing_the_entrance_leaves_the_rest_of_the_dungeon_alone() -> void:
+	# It skips the few enemies that would be awake on arrival and nothing else:
+	# the dungeon keeps nearly all of its population.
+	var total := 0
+	for s in range(1, 40):
+		total += Instance.make_dungeon(2, s * 7919, 1).world.enemies.size()
+	assert_gt(float(total) / 39.0, 9.0, "a depth-1 dungeon still has a dungeon's worth of enemies")