diff --git a/libdlfind/callback.py b/libdlfind/callback.py
index a44af41..689de0e 100644
--- a/libdlfind/callback.py
+++ b/libdlfind/callback.py
@@ -66,7 +66,7 @@ def wrapper(
         status: pointer[c_int],
     ) -> None:
         coords_ = as_array(coords, shape=(nvar,)).reshape((-1, 3))
-        hessian_ = as_array(hessian, shape=(nvar,))
+        hessian_ = as_array(hessian, shape=(nvar,nvar))
         hessian = func(coords_)
         hessian_[:, :] = hessian
         status[0] = c_int(0)
diff --git a/src/mod_api.f90 b/src/mod_api.f90
index 49d8178..b503436 100644
--- a/src/mod_api.f90
+++ b/src/mod_api.f90
@@ -46,7 +46,7 @@ subroutine dlf_get_hessian_interface(nvar, coords, hessian, status) bind(c)
       import c_double, c_int
 
       implicit none
-      integer(c_int), intent(in) :: nvar
+      integer(c_int), intent(in), value :: nvar
       real(c_double), intent(in) :: coords(nvar)
       real(c_double), intent(out) :: hessian(nvar, nvar)
       integer, intent(out) :: status