diff --git a/AMDiS/src/MatrixVector.h b/AMDiS/src/MatrixVector.h
index 521e5ca1e9ef00b709d3d021961f7f1a010a4d9d..c628f452029f1615ea5d0ae241b357a462b4e7fb 100644
--- a/AMDiS/src/MatrixVector.h
+++ b/AMDiS/src/MatrixVector.h
@@ -166,7 +166,7 @@ namespace AMDiS {
     /// Access to the i-th vector element.
     inline T& operator[](int i) 
     {
-      TEST_EXIT_DBG(i < size && i >= 0)("invalid index\n");
+      TEST_EXIT_DBG(i < size && i >= 0)("Invalid index %d!\n", i);
       return valArray[i];
     }