diff --git a/src/mesh/FEM_utilities.f90 b/src/mesh/FEM_utilities.f90
index 3bdf901e5..c97c2bbe2 100644
--- a/src/mesh/FEM_utilities.f90
+++ b/src/mesh/FEM_utilities.f90
@@ -69,7 +69,7 @@ module FEM_utilities
     type(tComponentBC), allocatable, dimension(:) :: componentBC
   end type tFieldBC
 
-  external :: &
+  external :: &                                                                                     ! ToDo: write interfaces
     PetscSectionGetFieldComponents, &
     PetscSectionGetFieldDof, &
     PetscSectionGetFieldOffset
diff --git a/src/mesh/discretization_mesh.f90 b/src/mesh/discretization_mesh.f90
index bbb125887..a53c50655 100644
--- a/src/mesh/discretization_mesh.f90
+++ b/src/mesh/discretization_mesh.f90
@@ -57,6 +57,9 @@ module discretization_mesh
     mesh_ipCoordinates                                                                              !< IP x,y,z coordinates (after deformation!)
 
   external :: &
+#ifdef PETSC_USE_64BIT_INDICES
+    DMDestroy, &
+#endif
     DMView                                                                                          ! ToDo: write interface
   public :: &
     discretization_mesh_init, &
@@ -248,10 +251,10 @@ subroutine mesh_FEM_build_ipCoordinates(dimPlex,qPoints)
     call DMPlexComputeCellGeometryAffineFEM(geomMesh,cell,pV0,pCellJ,pInvcellJ,detJ,err_PETSc)
     CHKERRQ(err_PETSc)
     qOffset = 0
-    do qPt = 1, mesh_maxNips
-      do dirI = 1, dimPlex
+    do qPt = 1_pPETSCINT, mesh_maxNips
+      do dirI = 1_pPETSCINT, dimPlex
         mesh_ipCoordinates(dirI,qPt,cell+1) = pV0(dirI)
-        do dirJ = 1, dimPlex
+        do dirJ = 1_pPETSCINT, dimPlex
           mesh_ipCoordinates(dirI,qPt,cell+1) = mesh_ipCoordinates(dirI,qPt,cell+1) + &
                                                 pCellJ((dirI-1)*dimPlex+dirJ)*(qPoints(qOffset+dirJ) + 1.0_pReal)
         enddo
diff --git a/src/mesh/mesh_mech_FEM.f90 b/src/mesh/mesh_mech_FEM.f90
index fae906891..e60d0213c 100644
--- a/src/mesh/mesh_mech_FEM.f90
+++ b/src/mesh/mesh_mech_FEM.f90
@@ -71,7 +71,7 @@ module mesh_mechanical_FEM
   logical :: ForwardData
   real(pReal), parameter :: eps = 1.0e-18_pReal
 
-  external :: &
+  external :: &                                                                                     ! ToDo: write interfaces
     PetscSectionGetNumFields, &
     PetscFESetQuadrature, &
     PetscFEGetDimension, &