diff --git a/core/CCMultiSet.ml b/core/CCMultiSet.ml
index 8e840586..3fa4c8c1 100644
--- a/core/CCMultiSet.ml
+++ b/core/CCMultiSet.ml
@@ -45,6 +45,12 @@ module type S = sig
 
   val remove : t -> elt -> t
 
+  val add_mult : t -> elt -> int -> t
+
+  val remove_mult : t -> elt -> int -> t
+
+  val update : t -> elt -> (int -> int) -> t
+
   val min : t -> elt
 
   val max : t -> elt
@@ -102,12 +108,31 @@ module Make(O : Set.OrderedType) = struct
     let n = count ms x in
     M.add x (n+1) ms
 
-  let remove ms x =
+  let add_mult ms x n =
+    if n < 0 then invalid_arg "CCMultiSet.add_mult";
+    if n=0
+      then ms
+      else M.add x (count ms x + n) ms
+
+  let remove_mult ms x n =
+    if n < 0 then invalid_arg "CCMultiSet.remove_mult";
+    let cur_n = count ms x in
+    let new_n = cur_n - n in
+    if new_n <= 0
+      then M.remove x ms
+      else M.add x new_n ms
+
+  let remove ms x = remove_mult ms x 1
+
+  let update ms x f =
     let n = count ms x in
-    match n with
-    | 0 -> ms
-    | 1 -> M.remove x ms
-    | _ -> M.add x (n-1) ms
+    match f n with
+    | 0 ->
+        if n=0 then ms else M.remove x ms
+    | n' ->
+        if n' < 0
+          then invalid_arg "CCMultiSet.udpate"
+          else M.add x n' ms
 
   let min ms =
     fst (M.min_binding ms)
@@ -197,3 +222,12 @@ module Make(O : Set.OrderedType) = struct
     seq (fun x -> m := add !m x);
     !m
 end
+
+(*$T
+  let module S = CCMultiSet.Make(String) in \
+    S.count (S.add_mult S.empty "a" 5) "a" = 5
+  let module S = CCMultiSet.Make(String) in \
+    S.count (S.remove_mult (S.add_mult S.empty "a" 5) "a" 3) "a" = 2
+  let module S = CCMultiSet.Make(String) in \
+    S.count (S.remove_mult (S.add_mult S.empty "a" 4) "a" 6) "a" = 0
+*)
diff --git a/core/CCMultiSet.mli b/core/CCMultiSet.mli
index 89d32f83..826f394b 100644
--- a/core/CCMultiSet.mli
+++ b/core/CCMultiSet.mli
@@ -45,6 +45,23 @@ module type S = sig
 
   val remove : t -> elt -> t
 
+  val add_mult : t -> elt -> int -> t
+  (** [add_mult set x n] adds [n] occurrences of [x] to [set]
+      @raise Invalid_argument if [n < 0]
+      @since NEXT_RELEASE *)
+
+  val remove_mult : t -> elt -> int -> t
+  (** [remove_mult set x n] removes at most [n] occurrences of [x] from [set]
+      @raise Invalid_argument if [n < 0]
+      @since NEXT_RELEASE *)
+
+  val update : t -> elt -> (int -> int) -> t
+  (** [update set x f] calls [f n] where [n] is the current multiplicity
+      of [x] in [set] ([0] to indicate its absence); the result of [f n]
+      is the new multiplicity of [x].
+      @raise Invalid_argument if [f n < 0]
+      @since NEXT_RELEASE *)
+
   val min : t -> elt
   (** Minimal element w.r.t the total ordering on elements *)