diff --git a/lib/elixir/lib/map_set.ex b/lib/elixir/lib/map_set.ex
index 67bd429a1c8..fbfd9c303c1 100644
--- a/lib/elixir/lib/map_set.ex
+++ b/lib/elixir/lib/map_set.ex
@@ -57,7 +57,8 @@ defmodule MapSet do
 
   # We don't use @opaque (or `:sets.set` which is opaque) because MapSets can be inlined,
   # either via module attributes or by the compiler.
-  @typep internal(value) :: %{optional(value) => term()}
+  # Defaulting to a broad `term()` type to prevent opaqueness violations.
+  @typep internal(_value) :: term()
 
   @type t(value) :: %__MODULE__{map: internal(value)}
   @type t :: t(term)
diff --git a/lib/elixir/test/elixir/fixtures/dialyzer/opaqueness.ex b/lib/elixir/test/elixir/fixtures/dialyzer/opaqueness.ex
index d8371c386e5..177c5f35f8f 100644
--- a/lib/elixir/test/elixir/fixtures/dialyzer/opaqueness.ex
+++ b/lib/elixir/test/elixir/fixtures/dialyzer/opaqueness.ex
@@ -14,6 +14,11 @@ defmodule Dialyzer.Opaqueness do
     bar(@my_set)
   end
 
+  def contains?(ids, id) do
+    id_set = MapSet.new(ids)
+    MapSet.member?(id_set, id)
+  end
+
   # Task.Supervisor returns a Task.t() containing an opaque Task.ref()
   @spec run_task() :: Task.t()
   def run_task do