diff --git a/spatialmap.cpp b/spatialmap.cpp
index 2c11aa0..ab6fff9 100644
--- a/spatialmap.cpp
+++ b/spatialmap.cpp
@@ -7,8 +7,10 @@ using DinkyECS::Entity;
 
 void SpatialMap::insert(Point pos, Entity ent, bool has_collision) {
   if(has_collision) {
+    dbc::check(!yes_collision.contains(pos), "YES_collision already has entity");
     yes_collision.insert_or_assign(pos, ent);
   } else {
+    dbc::check(!no_collision.contains(pos), "no_collision already has entity");
     no_collision.insert_or_assign(pos, ent);
   }
 }
@@ -18,12 +20,14 @@ bool SpatialMap::remove(Point pos) {
     yes_collision.erase(pos);
     return true;
   } else {
+    dbc::check(no_collision.contains(pos), "remove of entity that's not in no_collision");
     no_collision.erase(pos);
     return false;
   }
 }
 
 void SpatialMap::move(Point from, Point to, Entity ent) {
+  dbc::check(!occupied(to), "attempt to move to point with an existing entity");
   bool has_collision = remove(from);
   insert(to, ent, has_collision);
 }
diff --git a/worldbuilder.cpp b/worldbuilder.cpp
index 37f552e..a800f5f 100644
--- a/worldbuilder.cpp
+++ b/worldbuilder.cpp
@@ -69,7 +69,7 @@ bool WorldBuilder::find_open_spot(Point& pos_out) {
     for(matrix::rando_box it{$map.walls(), pos_out.x, pos_out.y, i}; it.next();) {
       Point test{size_t(it.x), size_t(it.y)};
 
-      if($map.can_move(test) && !$collision.occupied(test)) {
+      if($map.can_move(test) && !$collision.something_there(test)) {
         pos_out = test;
         return true;
       }
@@ -210,6 +210,7 @@ void WorldBuilder::place_entities(DinkyECS::World &world) {
     dbc::check(placed, "WorldBuild.find_open_spot also failed to position player");
 
     world.set<Position>(player.entity, player_pos);
+    $collision.insert(player_pos.location, player.entity, true);
   } else {
     auto player_data = config.enemies["PLAYER_TILE"];
     auto player_ent = configure_entity_in_room(world, player_data, 0);