1 files changed, 9 insertions, 1 deletions
diff --git a/src/RK4.c b/src/RK4.c
index 55a4a4e..f0ebc8f 100644
--- a/src/RK4.c
+++ b/src/RK4.c
@@ -100,6 +100,8 @@ CCTK_WARN(0, "not implemented");
      we know the "real" alpha (including round-off errors) when we
      calculate the final result. */
   static CCTK_REAL sum_alpha;
+  /* the last MoL intermediate step that was summed */
+  static CCTK_INT last_sum_step;
 
   totalsize = 1;
   for (arraydim = 0; arraydim < cctk_dim; arraydim++)
@@ -134,8 +136,14 @@ CCTK_WARN(0, "not implemented");
   if (MoL_Intermediate_Steps == (*MoL_Intermediate_Step))
   {
     sum_alpha = 0.0;
+    last_sum_step = -1;
+  }
+  /* Add alpha once per intermediate step */
+  if (last_sum_step != (*MoL_Intermediate_Step))
+  {
+    sum_alpha += alpha;
+    last_sum_step = (*MoL_Intermediate_Step);
   }
-  sum_alpha += alpha;
 
   /* FIXME */