diff --git a/compiler/dcalc/interpreter.ml b/compiler/dcalc/interpreter.ml
index 1ba6a92e..f4e9663e 100644
--- a/compiler/dcalc/interpreter.ml
+++ b/compiler/dcalc/interpreter.ml
@@ -108,13 +108,13 @@ let rec evaluate_operator
     A.ELit (LDuration Runtime.(d1 -@ d2))
   | A.Binop (A.Add KDate), [ELit (LDate d1); ELit (LDuration d2)] ->
     A.ELit (LDate Runtime.(d1 +@ d2))
-  | A.Binop (A.Div KDuration), [ELit (LDuration d1); ELit (LDuration d2)] ->
-    apply_div_or_raise_err (fun _ ->
-        try A.ELit (LRat Runtime.(d1 /^ d2))
-        with Runtime.IndivisableDurations ->
-          Errors.raise_multispanned_error (get_binop_args_pos args)
-            "Cannot divide durations that cannot be converted to a precise \
-             number of days")
+  (* | A.Binop (A.Div KDuration), [ELit (LDuration d1); ELit (LDuration d2)] ->
+   *   apply_div_or_raise_err (fun _ ->
+   *       try A.ELit (LRat Runtime.(d1 /^ d2))
+   *       with Runtime.IndivisableDurations ->
+   *         Errors.raise_multispanned_error (get_binop_args_pos args)
+   *           "Cannot divide durations that cannot be converted to a precise \
+   *            number of days") *)
   | A.Binop (A.Mult KDuration), [ELit (LDuration d1); ELit (LInt i1)] ->
     A.ELit (LDuration Runtime.(d1 *^ i1))
   | A.Binop (A.Lt KInt), [ELit (LInt i1); ELit (LInt i2)] ->
@@ -253,10 +253,10 @@ let rec evaluate_operator
   | A.Unop A.GetMonth, [ELit (LDate d)] ->
     A.ELit (LInt Runtime.(month_number_of_date d))
   | A.Unop A.GetYear, [ELit (LDate d)] -> A.ELit (LInt Runtime.(year_of_date d))
-  | A.Unop A.FirstDayOfMonth, [ELit (LDate d)] ->
-    A.ELit (LDate Runtime.(first_day_of_month d))
-  | A.Unop A.LastDayOfMonth, [ELit (LDate d)] ->
-    A.ELit (LDate Runtime.(first_day_of_month d))
+  (* | A.Unop A.FirstDayOfMonth, [ELit (LDate d)] ->
+   *   A.ELit (LDate Runtime.(first_day_of_month d))
+   * | A.Unop A.LastDayOfMonth, [ELit (LDate d)] ->
+   *   A.ELit (LDate Runtime.(first_day_of_month d)) *)
   | A.Unop A.IntToRat, [ELit (LInt i)] ->
     A.ELit (LRat Runtime.(decimal_of_integer i))
   | A.Unop A.MoneyToRat, [ELit (LMoney i)] ->
@@ -323,7 +323,6 @@ let rec evaluate_operator
           args)
       "Operator applied to the wrong arguments\n\
        (should not happen if the term was well-typed)"
->>>>>>> master
 
 and evaluate_expr (ctx : Ast.decl_ctx) (e : 'm A.marked_expr) : 'm A.marked_expr
     =
diff --git a/compiler/verification/z3backend.real.ml b/compiler/verification/z3backend.real.ml
index eb074c8d..3c8c649c 100644
--- a/compiler/verification/z3backend.real.ml
+++ b/compiler/verification/z3backend.real.ml
@@ -19,6 +19,7 @@ open Dcalc
 open Ast
 open Z3
 module StringMap : Map.S with type key = String.t = Map.Make (String)
+module Runtime = Runtime_ocaml.Runtime
 
 type context = {
   ctx_z3 : Z3.context;
@@ -95,7 +96,7 @@ let add_z3constraint (e : Expr.expr) (ctx : context) : context =
 
 (** For the Z3 encoding of Catala programs, we define the "day 0" as Jan 1, 1900
     **)
-let base_day = CalendarLib.Date.make 1900 1 1
+let base_day = Dates_calc.Dates.make_date ~year:1900 ~month:1 ~day:1
 
 (** [unique_name] returns the full, unique name corresponding to variable [v],
     as given by Bindlib **)
@@ -107,11 +108,10 @@ let unique_name (v : 'm var) : string =
 let date_to_int (d : Runtime.date) : int =
   (* Alternatively, could expose this from Runtime as a (noop) coercion, but
      would allow to break abstraction more easily elsewhere *)
-  let date : CalendarLib.Date.t =
-    CalendarLib.Printer.Date.from_string (Runtime.date_to_string d)
-  in
-  let period = CalendarLib.Date.sub date base_day in
-  CalendarLib.Date.Period.nb_days period
+  let period = Runtime.( -@ ) d base_day in
+  let y, m, d = Runtime.duration_to_string period in
+  assert (y = 0 && m = 0);
+  d
 
 (** [date_of_year] translates a [year], represented as an integer into an OCaml
     date corresponding to Jan 1st of the same year *)
@@ -120,8 +120,8 @@ let date_of_year (year : int) = Runtime.date_of_numbers year 1 1
 (** Returns the date (as a string) corresponding to nb days after the base day,
     defined here as Jan 1, 1900 **)
 let nb_days_to_date (nb : int) : string =
-  CalendarLib.Printer.Date.to_string
-    (CalendarLib.Date.add base_day (CalendarLib.Date.Period.day nb))
+  Runtime.date_to_string
+    (Runtime.( +@ ) base_day (Runtime.duration_of_numbers 0 0 nb))
 
 (** [print_z3model_expr] pretty-prints the value [e] given by a Z3 model
     according to the Catala type [ty], corresponding to [e] **)
diff --git a/runtimes/ocaml/runtime.mli b/runtimes/ocaml/runtime.mli
index d978f3bd..f518455b 100644
--- a/runtimes/ocaml/runtime.mli
+++ b/runtimes/ocaml/runtime.mli
@@ -252,8 +252,8 @@ val date_of_numbers : int -> int -> int -> date
 
     @raise ImpossibleDate *)
 
-val first_day_of_month : date -> date
-val last_day_of_month : date -> date
+(* val first_day_of_month : date -> date
+ * val last_day_of_month : date -> date *)
 
 (**{2 Durations} *)