diff --git a/src/grid/spectral_utilities.f90 b/src/grid/spectral_utilities.f90
index 525f68d7e..4375ec860 100644
--- a/src/grid/spectral_utilities.f90
+++ b/src/grid/spectral_utilities.f90
@@ -142,7 +142,7 @@ contains
 !> level chosen.
 !> Initializes FFTW.
 !--------------------------------------------------------------------------------------------------
-subroutine spectral_utilities_init
+subroutine spectral_utilities_init()
 
   PetscErrorCode :: err_PETSc
   integer        :: i, j, k, &
@@ -350,6 +350,8 @@ subroutine spectral_utilities_init
     allocate (gamma_hat(3,3,3,3,cells1Red,cells(2),cells3), source = cmplx(0.0_pReal,0.0_pReal,pReal))
   endif
 
+  call selfTest()
+
 end subroutine spectral_utilities_init
 
 
@@ -1146,4 +1148,41 @@ subroutine utilities_saveReferenceStiffness
 
 end subroutine utilities_saveReferenceStiffness
 
+
+!--------------------------------------------------------------------------------------------------
+!> @brief Check correctness of forward-backward transform.
+!--------------------------------------------------------------------------------------------------
+subroutine selfTest()
+
+  real(pReal), allocatable, dimension(:,:,:,:,:) :: tensorField_real_
+  real(pReal), allocatable, dimension(:,:,:,:) :: vectorField_real_
+  real(pReal), allocatable, dimension(:,:,:) :: scalarField_real_
+
+
+  call random_number(tensorField_real)
+  tensorField_real(1:3,1:3,cells(1)+1:cells1Red*2,:,:) = 0.0_pReal
+  tensorField_real_ = tensorField_real
+  call utilities_FFTtensorForward()
+  call utilities_FFTtensorBackward()
+  tensorField_real(1:3,1:3,cells(1)+1:cells1Red*2,:,:) = 0.0_pReal
+  if (maxval(abs(tensorField_real_ - tensorField_real))>5.0e-15_pReal) error stop 'tensorField'
+
+  call random_number(vectorField_real)
+  vectorField_real(1:3,cells(1)+1:cells1Red*2,:,:) = 0.0_pReal
+  vectorField_real_ = vectorField_real
+  call utilities_FFTvectorForward()
+  call utilities_FFTvectorBackward()
+  vectorField_real(1:3,cells(1)+1:cells1Red*2,:,:) = 0.0_pReal
+  if (maxval(abs(vectorField_real_ - vectorField_real))>5.0e-15_pReal) error stop 'vectorField'
+
+  call random_number(scalarField_real)
+  scalarField_real(cells(1)+1:cells1Red*2,:,:) = 0.0_pReal
+  scalarField_real_ = scalarField_real
+  call utilities_FFTscalarForward()
+  call utilities_FFTscalarBackward()
+  scalarField_real(cells(1)+1:cells1Red*2,:,:) = 0.0_pReal
+  if (maxval(abs(scalarField_real_ - scalarField_real))>5.0e-15_pReal) error stop 'scalarField'
+
+end subroutine selfTest
+
 end module spectral_utilities
diff --git a/src/prec.f90 b/src/prec.f90
index d0753790e..73563d4f2 100644
--- a/src/prec.f90
+++ b/src/prec.f90
@@ -48,7 +48,7 @@ contains
 !--------------------------------------------------------------------------------------------------
 !> @brief Report precision and do self test.
 !--------------------------------------------------------------------------------------------------
-subroutine prec_init
+subroutine prec_init()
 
   print'(/,1x,a)', '<<<+-  prec init  -+>>>'
 
@@ -60,7 +60,7 @@ subroutine prec_init
   print'(  a,e10.3)', '   epsilon value:      ',PREAL_EPSILON
   print'(  a,i3)',    '   decimal precision:  ',precision(0.0_pReal)
 
-  call selfTest
+  call selfTest()
 
 end subroutine prec_init
 
@@ -245,7 +245,7 @@ end function prec_bytesToC_INT64_T
 !--------------------------------------------------------------------------------------------------
 !> @brief Check correctness of some prec functions.
 !--------------------------------------------------------------------------------------------------
-subroutine selfTest
+subroutine selfTest()
 
   integer, allocatable, dimension(:) :: realloc_lhs_test
   real(pReal),   dimension(1) :: f