diff --git a/src/ao_basis/aos.irp.f b/src/ao_basis/aos.irp.f
index d2ce1ab2..1cbd3976 100644
--- a/src/ao_basis/aos.irp.f
+++ b/src/ao_basis/aos.irp.f
@@ -21,6 +21,21 @@ BEGIN_PROVIDER [ integer, ao_shell, (ao_num) ]
    enddo
  enddo
 
+END_PROVIDER
+
+BEGIN_PROVIDER [ integer, ao_first_of_shell, (shell_num) ]
+ implicit none
+ BEGIN_DOC
+ ! Index of the shell to which the AO corresponds
+ END_DOC
+ integer :: i, j, k, n
+ k=1
+ do i=1,shell_num
+   ao_first_of_shell(i) = k
+   n = shell_ang_mom(i)+1
+   k = k+(n*(n+1))/2
+ enddo
+
 END_PROVIDER
 
  BEGIN_PROVIDER [ double precision, ao_coef_normalized, (ao_num,ao_prim_num_max) ]
diff --git a/src/basis/EZFIO.cfg b/src/basis/EZFIO.cfg
index 7f2ede4c..a6df8e7a 100644
--- a/src/basis/EZFIO.cfg
+++ b/src/basis/EZFIO.cfg
@@ -39,7 +39,7 @@ interface: ezfio, provider
 
 [shell_prim_index]
 type: integer
-doc: Max number of primitives in a shell
+doc: Index of the first primitive of the shell
 size: (basis.shell_num)
 interface: ezfio, provider