diff --git a/include/laser_geometry/laser_geometry.h b/include/laser_geometry/laser_geometry.h
index f58d4b1..8610915 100644
--- a/include/laser_geometry/laser_geometry.h
+++ b/include/laser_geometry/laser_geometry.h
@@ -35,6 +35,7 @@
 #include <sstream>
 
 #include "boost/numeric/ublas/matrix.hpp"
+#include "boost/thread/mutex.hpp"
 
 #include "tf/tf.h"
 
@@ -234,6 +235,7 @@ namespace laser_geometry
       //! Internal map of pointers to stored values
       std::map<std::string,boost::numeric::ublas::matrix<double>* > unit_vector_map_;
 
+      boost::mutex guv_mutex_;
     };
 
 }
diff --git a/src/laser_geometry.cpp b/src/laser_geometry.cpp
index a2ed1e1..ab60bb5 100644
--- a/src/laser_geometry.cpp
+++ b/src/laser_geometry.cpp
@@ -152,6 +152,8 @@ namespace laser_geometry
 
 const boost::numeric::ublas::matrix<double>& LaserProjection::getUnitVectors_(double angle_min, double angle_max, double angle_increment, unsigned int length)
   {
+    boost::mutex::scoped_lock guv_lock(this->guv_mutex_);
+
     //construct string for lookup in the map
     std::stringstream anglestring;
     anglestring <<angle_min<<","<<angle_max<<","<<angle_increment<<","<<length;