diff --git a/src/cdomains/apron/affineEqualityDomain.apron.ml b/src/cdomains/apron/affineEqualityDomain.apron.ml
index 6c5112c279..9febdb5778 100644
--- a/src/cdomains/apron/affineEqualityDomain.apron.ml
+++ b/src/cdomains/apron/affineEqualityDomain.apron.ml
@@ -53,7 +53,7 @@ struct
   let copy t = {t with d = Option.map Matrix.copy t.d}
 
   let dim_add (ch: Apron.Dim.change) m =
-    Array.iteri (fun i x -> ch.dim.(i) <- x + i) ch.dim;
+    Array.modifyi (fun i x -> x + i) ch.dim; (* could be written Array.modifyi (+) ch.dim; but that's too smart *)
     Matrix.add_empty_columns m ch.dim
 
   let dim_add ch m = timing_wrap "dim add" (dim_add ch) m
@@ -62,7 +62,7 @@ struct
     if Array.length ch.dim = 0 || Matrix.is_empty m then 
       m 
     else (
-      Array.iteri (fun i x-> ch.dim.(i) <- x + i) ch.dim;
+      Array.modifyi (fun i x -> x + i) ch.dim;
       let m' = if not del then let m = Matrix.copy m in Array.fold_left (fun y x -> Matrix.reduce_col_with y x; y) m ch.dim else m in
       Matrix.remove_zero_rows @@ Matrix.del_cols m' ch.dim)