diff --git a/README.md b/README.md
index 28c7bfc..4c5c229 100644
--- a/README.md
+++ b/README.md
@@ -181,7 +181,7 @@ polymorphic_embeds_many :contexts,
   By default, a changeset error "is invalid" is added.
 * `:on_replace` – mandatory option that can only be set to `:update` for a single embed and `:delete` for a list of
   embeds (we force a value as the default value of this option for `embeds_one` and `embeds_many` is `:raise`).
-* `:retain_unlisted_types_on_load`: allow unconfigured types to be loaded without raising an error. Useful for handling deprecated structs still present in the database.
+* `:retain_unlisted_types_on_load`: allow unconfigured types to be loaded without raising an error. Useful for handling deprecated structs still present in the database. Pass `:all` to retain every type the field does not know, e.g. when several application versions share a database during a rolling deploy, or a type was removed without migrating its rows; the data then loads as the raw map. A raw map cannot be dumped back, so treat such records as read-only.
 * `:nilify_unlisted_types_on_load`: same as `:retain_unlisted_types_on_load`, but nilify the struct on load.
 
 ### Displaying form inputs and errors in Phoenix templates
diff --git a/lib/polymorphic_embed.ex b/lib/polymorphic_embed.ex
index 47e8ad9..3d0bdb8 100644
--- a/lib/polymorphic_embed.ex
+++ b/lib/polymorphic_embed.ex
@@ -491,7 +491,10 @@ defmodule PolymorphicEmbed do
     case get_polymorphic_module_from_map(data, type_field_name, types_metadata) do
       nil ->
         retain_type_list =
-          Map.fetch!(field_opts, :retain_unlisted_types_on_load) |> Enum.map(&to_string(&1))
+          case Map.fetch!(field_opts, :retain_unlisted_types_on_load) do
+            :all -> :all
+            types -> Enum.map(types, &to_string(&1))
+          end
 
         nilify_type_list =
           Map.fetch!(field_opts, :nilify_unlisted_types_on_load) |> Enum.map(&to_string(&1))
@@ -499,7 +502,7 @@ defmodule PolymorphicEmbed do
         type = Map.get(data, type_field_name |> to_string)
 
         cond do
-          type in retain_type_list ->
+          retain_type_list == :all or type in retain_type_list ->
             {:ok, data}
 
           type in nilify_type_list ->
diff --git a/lib/polymorphic_embed/options_validator.ex b/lib/polymorphic_embed/options_validator.ex
index 8ef81db..19ef824 100644
--- a/lib/polymorphic_embed/options_validator.ex
+++ b/lib/polymorphic_embed/options_validator.ex
@@ -61,8 +61,9 @@ defmodule PolymorphicEmbed.OptionsValidator do
     retain_unlisted_types = Keyword.fetch!(options, :retain_unlisted_types_on_load)
     nilify_unlisted_types = Keyword.fetch!(options, :nilify_unlisted_types_on_load)
 
-    unless is_list(retain_unlisted_types) and Enum.all?(retain_unlisted_types, &is_atom/1) do
-      raise "`:retain_unlisted_types_on_load` option must be a list of types as atoms."
+    unless retain_unlisted_types == :all or
+             (is_list(retain_unlisted_types) and Enum.all?(retain_unlisted_types, &is_atom/1)) do
+      raise "`:retain_unlisted_types_on_load` option must be :all or a list of types as atoms."
     end
 
     unless is_list(nilify_unlisted_types) and Enum.all?(nilify_unlisted_types, &is_atom/1) do
diff --git a/test/polymorphic_embed_test.exs b/test/polymorphic_embed_test.exs
index ba50279..9de6191 100644
--- a/test/polymorphic_embed_test.exs
+++ b/test/polymorphic_embed_test.exs
@@ -1696,6 +1696,59 @@ defmodule PolymorphicEmbedTest do
              |> Repo.one()
   end
 
+  describe "retain_unlisted_types_on_load: :all" do
+    defp retain_all_params(retain) do
+      PolymorphicEmbed.init(
+        field: :channel,
+        schema: PolymorphicEmbed.Reminder,
+        array?: false,
+        default: nil,
+        types: [sms: PolymorphicEmbed.Channel.SMS],
+        on_replace: :update,
+        type_field_name: :my_type_field,
+        retain_unlisted_types_on_load: retain
+      )
+    end
+
+    test "loads any type the field does not know as the raw map" do
+      params = retain_all_params(:all)
+
+      for type <- ["some_deprecated_type", "a_type_from_a_newer_release"] do
+        data = %{"my_type_field" => type, "number" => "02/807.05.53"}
+        assert {:ok, ^data} = PolymorphicEmbed.load(data, &Ecto.Type.load/2, params)
+      end
+    end
+
+    test "still loads a known type as its struct" do
+      params = retain_all_params(:all)
+      data = %{"my_type_field" => "sms", "number" => "02/807.05.53", "country_code" => 1}
+
+      assert {:ok, %PolymorphicEmbed.Channel.SMS{number: "02/807.05.53"}} =
+               PolymorphicEmbed.load(data, &Ecto.Type.load/2, params)
+    end
+
+    test "a list keeps retaining only the listed types" do
+      params = retain_all_params([:some_deprecated_type])
+
+      assert {:ok, _} =
+               PolymorphicEmbed.load(
+                 %{"my_type_field" => "some_deprecated_type"},
+                 &Ecto.Type.load/2,
+                 params
+               )
+
+      assert_raise RuntimeError, fn ->
+        PolymorphicEmbed.load(%{"my_type_field" => "unlisted"}, &Ecto.Type.load/2, params)
+      end
+    end
+
+    test "rejects anything other than :all or a list of atoms" do
+      assert_raise RuntimeError, ~r/must be :all or a list of types as atoms/, fn ->
+        retain_all_params(:some)
+      end
+    end
+  end
+
   test "changing type" do
     generator = :polymorphic
     reminder_module = get_module(Reminder, generator)