diff --git a/vcg/math/lin_algebra.h b/vcg/math/lin_algebra.h
index 251a5fe8..d842c6da 100644
--- a/vcg/math/lin_algebra.h
+++ b/vcg/math/lin_algebra.h
@@ -1,3 +1,6 @@
+#ifndef __VCGLIB_LINALGEBRA_H
+#define __VCGLIB_LINALGEBRA_H
+
 #include <vcg/math/matrix44.h>
 
 namespace vcg
@@ -435,4 +438,6 @@ namespace vcg
 	};
 
 	/*! @} */
-}; // end of namespace
\ No newline at end of file
+}; // end of namespace
+
+#endif
\ No newline at end of file