diff --git a/src/scf_module.F90 b/src/scf_module.F90
index 8ddeb86ea..7098dbb68 100644
--- a/src/scf_module.F90
+++ b/src/scf_module.F90
@@ -336,6 +336,10 @@ subroutine scf(env, mol, wfn, basis, pcem, xtbData, solvation, &
 
    ! fill levels
    if(wfn%nel.ne.0) then
+      if (wfn%nel > 2*basis%nao) then
+         call env%error("Not enough basis functions for filling orbitals", source)
+         return
+      end if
       call occu(basis%nao,wfn%nel,wfn%nopen,wfn%ihomoa,wfn%ihomob,wfn%focca,wfn%foccb)
       wfn%focc = wfn%focca + wfn%foccb
       wfn%ihomo=wfn%ihomoa