diff --git a/simgear/scene/material/matlib.cxx b/simgear/scene/material/matlib.cxx
index 2ff1624e..bbf58b32 100644
--- a/simgear/scene/material/matlib.cxx
+++ b/simgear/scene/material/matlib.cxx
@@ -83,6 +83,8 @@ bool SGMaterialLib::load( const SGPath &fg_root, const SGPath& mpath,
     options->setObjectCacheHint(osgDB::Options::CACHE_ALL);
     options->setDatabasePath(fg_root.utf8Str());
 
+    std::lock_guard<std::mutex> g(d->mutex);
+
     simgear::PropertyList blocks = materialblocks.getChildren("region");
     simgear::PropertyList::const_iterator block_iter = blocks.begin();
 
@@ -153,14 +155,20 @@ bool SGMaterialLib::load( const SGPath &fg_root, const SGPath& mpath,
 
 // find a material record by material name and tile center
 SGMaterial *SGMaterialLib::find( const string& material, const SGVec2f center ) const
+{
+    std::lock_guard<std::mutex> g(d->mutex);
+    return internalFind(material, center);
+}
+
+SGMaterial* SGMaterialLib::internalFind(const string& material, const SGVec2f center) const
 {
     SGMaterial *result = NULL;
     const_material_map_iterator it = matlib.find( material );
-    if ( it != end() ) {            
+    if (it != end()) {
         // We now have a list of materials that match this
         // name. Find the first one that matches.
-    	// We start at the end of the list, as the materials
-    	// list is ordered with the smallest regions at the end.
+        // We start at the end of the list, as the materials
+        // list is ordered with the smallest regions at the end.
         material_list::const_reverse_iterator iter = it->second.rbegin();
         while (iter != it->second.rend()) {
             result = *iter;
@@ -184,11 +192,12 @@ SGMaterial *SGMaterialLib::find( const string& material, const SGGeod& center )
 SGMaterialCache *SGMaterialLib::generateMatCache(SGVec2f center)
 {
 	SGMaterialCache* newCache = new SGMaterialCache();
+    std::lock_guard<std::mutex> g(d->mutex);
+
     material_map::const_reverse_iterator it = matlib.rbegin();
     for (; it != matlib.rend(); ++it) {
-        newCache->insert(it->first, find(it->first, center));
+        newCache->insert(it->first, internalFind(it->first, center));
     }
-    
     return newCache;
 }
 
diff --git a/simgear/scene/material/matlib.hxx b/simgear/scene/material/matlib.hxx
index ff80d795..d09c96d2 100644
--- a/simgear/scene/material/matlib.hxx
+++ b/simgear/scene/material/matlib.hxx
@@ -81,7 +81,10 @@ private:
     typedef material_map::const_iterator const_material_map_iterator;
 
     material_map matlib;
-    
+
+
+    SGMaterial* internalFind(const std::string& material, const SGVec2f center) const;
+
 public:
 
     // Constructor