diff --git a/src/Matrix.cc b/src/Matrix.cc
index 87dec24..f552ea8 100755
--- a/src/Matrix.cc
+++ b/src/Matrix.cc
@@ -982,7 +982,7 @@ public:
 
 private:
   Matrix* matrix;
-  char* filename;
+  std::string filename;
   int res;
 };