diff --git a/BaseLib/CPUTime.h b/BaseLib/CPUTime.h
index 6f0b18455741c93eb46114ac8059b5900d55c4c3..fc72f563a2ec2ee4c869172250723f2dd3fc8b80 100644
--- a/BaseLib/CPUTime.h
+++ b/BaseLib/CPUTime.h
@@ -32,7 +32,7 @@ class CPUTime
         }
 
         /// Get the elapsed time after started.
-        double elapsed()
+        const double elapsed()
         {
             return (clock() - _start_time)/static_cast<double>(CLOCKS_PER_SEC);
         }
diff --git a/BaseLib/RunTime.h b/BaseLib/RunTime.h
index bb55470e2e0c101e055be6af9d2fd7cd06933828..cb67269a0b4269a21113accc197b44c72497bbac 100644
--- a/BaseLib/RunTime.h
+++ b/BaseLib/RunTime.h
@@ -50,7 +50,7 @@ class RunTime
         }
 
         /// Get the elapsed time after started.
-        double elapsed()
+        const double elapsed()
         {
 #if defined(USE_MPI)
             return MPI_Wtime() - _start_time;
diff --git a/MathLib/LinAlg/PETSc/PETScLinearSolver.h b/MathLib/LinAlg/PETSc/PETScLinearSolver.h
index c908e914c93ecc7ea8af3fddaa2d4b3c0c5ec476..1496df53a59d5ce404f5e5ae2b0a0ff16943eaa8 100644
--- a/MathLib/LinAlg/PETSc/PETScLinearSolver.h
+++ b/MathLib/LinAlg/PETSc/PETScLinearSolver.h
@@ -23,7 +23,6 @@
 
 #include "PETScMatrix.h"
 #include "PETScVector.h"
-#include "BaseLib/PETScWallClockTimer.h"
 
 namespace MathLib
 {