diff --git a/library/terraman_library_merger_pcm.cpp b/library/terraman_library_merger_pcm.cpp
index 179ad0f..41b4c2f 100644
--- a/library/terraman_library_merger_pcm.cpp
+++ b/library/terraman_library_merger_pcm.cpp
@@ -101,7 +101,7 @@ void TerramanLibraryMergerPCM::_material_cache_get_key(Ref<TerraChunk> chunk) {
 	chunk->material_cache_key_set(hash);
 	chunk->material_cache_key_has_set(true);
 
-	_cache_mutex.lock();
+	_material_cache_mutex.lock();
 
 	if (_material_cache.has(hash)) {
 		Ref<TerraMaterialCachePCM> cc = _material_cache[hash];
@@ -110,7 +110,7 @@ void TerramanLibraryMergerPCM::_material_cache_get_key(Ref<TerraChunk> chunk) {
 			cc->inc_ref_count();
 		}
 
-		_cache_mutex.unlock();
+		_material_cache_mutex.unlock();
 
 		return;
 	}
@@ -162,7 +162,7 @@ void TerramanLibraryMergerPCM::_material_cache_get_key(Ref<TerraChunk> chunk) {
 	_material_cache[hash] = cache;
 
 	//unlock here, so if a different thread need the cache it will be able to immediately access the materials and surfaces when it gets it.
-	_cache_mutex.unlock();
+	_material_cache_mutex.unlock();
 
 	//this will generate the atlases
 	cache->refresh_rects();
@@ -179,7 +179,7 @@ Ref<TerraMaterialCache> TerramanLibraryMergerPCM::_material_cache_get(const int
 }
 
 void TerramanLibraryMergerPCM::_material_cache_unref(const int key) {
-	_cache_mutex.lock();
+	_material_cache_mutex.lock();
 
 	if (!_material_cache.has(key)) {
 		return;
@@ -197,7 +197,7 @@ void TerramanLibraryMergerPCM::_material_cache_unref(const int key) {
 		_material_cache.erase(key);
 	}
 
-	_cache_mutex.unlock();
+	_material_cache_mutex.unlock();
 }
 
 int TerramanLibraryMergerPCM::get_texture_flags() const {
diff --git a/library/terraman_library_merger_pcm.h b/library/terraman_library_merger_pcm.h
index 96a4076..2a94c58 100644
--- a/library/terraman_library_merger_pcm.h
+++ b/library/terraman_library_merger_pcm.h
@@ -54,6 +54,7 @@ class TerramanLibraryMergerPCM : public TerramanLibrary {
 
 public:
 	bool _supports_caching();
+
 	void _material_cache_get_key(Ref<TerraChunk> chunk);
 	Ref<TerraMaterialCache> _material_cache_get(const int key);
 	void _material_cache_unref(const int key);
@@ -125,7 +126,8 @@ protected:
 	Ref<TexturePacker> _packer;
 	Ref<TexturePacker> _prop_packer;
 
-	Mutex _cache_mutex;
+	Mutex _material_cache_mutex;
+	Mutex _prop_material_cache_mutex;
 };
 
 #endif