diff --git a/CI/F12CI.ml b/CI/F12CI.ml
index 9beb0f4..cc8497d 100644
--- a/CI/F12CI.ml
+++ b/CI/F12CI.ml
@@ -28,10 +28,9 @@ let f12_integrals mo_basis =
           and ijlk = F12.get_phys two_e_ints i j l k
           in
           if s' = Spin.other s then
-            0.375 *. ijkl +.  0.125 *. ijlk
-            (*
-            0.25 *. ijkl
-            *)
+            (* Minus sign because we swap spin variables
+               instead of orbital variables *)
+            0.375 *. ijkl -.  0.125 *. ijlk
           else
             0.25 *. (ijkl -. ijlk) 
         end