diff --git a/Utils/Util.ml b/Utils/Util.ml
index cecca3c..c19b4fc 100644
--- a/Utils/Util.ml
+++ b/Utils/Util.ml
@@ -6,7 +6,7 @@ let factmax = 150
 (** Generalized Boys function. Uses GSL's incomplete Gamma function.
     maxm : Maximum total angular momentum
 *)
-let boys_function ~maxm t =
+let rec boys_function ~maxm t =
   match maxm with
   | 0 ->
     begin
@@ -33,7 +33,12 @@ let boys_function ~maxm t =
           let (dm, f) = factor.(i-1) in
           factor.(i) <- (dm +. 1., f *. t_inv);
         done;
-        Array.map (fun (dm, f) -> (incomplete_gamma dm t ) *. 0.5 *. f) factor 
+        Array.map (fun (dm, f) ->
+          if dm = 0.5 then
+            (boys_function ~maxm:0 t).(0)
+          else
+            (incomplete_gamma dm t ) *. 0.5 *. f
+        ) factor 
     end