# UNDF: UNDF-2026-000000939
--- a/src/mapgen/mg_decoration.h
+++ b/src/mapgen/mg_decoration.h
@@ -50,9 +50,9 @@ class Decoration : public ObjDef, public NodeResolver {
 	u32 flags = 0;
 	int mapseed = 0;
-	std::vector<content_t> c_place_on;
+	std::unordered_set<content_t> c_place_on;
 	int check_offset = 0;
 	s16 sidelen = 2;
 	s16 y_min;
 	s16 y_max;
@@ -58,7 +58,7 @@ class Decoration : public ObjDef, public NodeResolver {
 	float fill_ratio = 0.0f;
 	NoiseParams np;
-	std::vector<content_t> c_spawnby;
+	std::unordered_set<content_t> c_spawnby;
 	s16 nspawnby = -1;
 	s16 place_offset_y = 0;
 	std::unordered_set<biome_t> biomes;
--- a/src/mapgen/mg_decoration.cpp
+++ b/src/mapgen/mg_decoration.cpp
@@ -60,8 +60,14 @@ void Decoration::resolveNodeNames()
 {
-	getIdsFromNrBacklog(&c_place_on);
-	getIdsFromNrBacklog(&c_spawnby);
+	std::vector<content_t> place_on_vec;
+	getIdsFromNrBacklog(&place_on_vec);
+	c_place_on.clear();
+	c_place_on.insert(place_on_vec.begin(), place_on_vec.end());
+
+	std::vector<content_t> spawnby_vec;
+	getIdsFromNrBacklog(&spawnby_vec);
+	c_spawnby.clear();
+	c_spawnby.insert(spawnby_vec.begin(), spawnby_vec.end());
 }

 bool Decoration::canPlaceDecoration(MMVManip *vm, v3s16 p)
@@ -72,7 +78,7 @@ bool Decoration::canPlaceDecoration(MMVManip *vm, v3s16 p)
 	// Check if the decoration can be placed on this node
 	u32 vi = vm->m_area.index(p);
-	if (!CONTAINS(c_place_on, vm->m_data[vi].getContent()))
+	if (c_place_on.count(vm->m_data[vi].getContent()) == 0)
 		return false;

@@ -98,7 +104,7 @@ bool Decoration::canPlaceDecoration(MMVManip *vm, v3s16 p)
 		if (!vm->m_area.contains(index))
 			continue;

-		if (CONTAINS(c_spawnby, vm->m_data[index].getContent()))
+		if (c_spawnby.count(vm->m_data[index].getContent()) > 0)
 			nneighs++;
 	}

@@ -110,7 +116,7 @@ bool Decoration::canPlaceDecoration(MMVManip *vm, v3s16 p)
 			if (!vm->m_area.contains(index))
 				continue;

-			if (CONTAINS(c_spawnby, vm->m_data[index].getContent()))
+			if (c_spawnby.count(vm->m_data[index].getContent()) > 0)
 				nneighs++;
 		}