diff --git a/lib/pleroma/web/activity_pub/mrf/block-invalid-datetime.ex b/lib/pleroma/web/activity_pub/mrf/block-invalid-datetime.ex
new file mode 100644
index 000000000..114a0c112
--- /dev/null
+++ b/lib/pleroma/web/activity_pub/mrf/block_invalid_datetime.ex
@@ -0,0 +1,51 @@
+defmodule Pleroma.Web.ActivityPub.MRF.BlockInvalidDatetime do
+  alias Pleroma.Web.CommonAPI
+  alias Pleroma.User
+
+  @moduledoc "Reports posts which have invalid datetime"
+
+  @behaviour Pleroma.Web.ActivityPub.MRF.Policy
+
+  def invalid_publish_date?(dt) do
+    # Only support publish dates back to 1583; ISO8601  only officially supports dates this far back
+    # And not past 9999 this may also cause issues lol
+    dt |> DateTime.compare(~U[1583-01-01 00:00:00Z]) == :lt ||
+      dt |> DateTime.compare(~U[9999-12-31 23:59:59Z]) == :gt
+  end
+
+  @impl true
+  def filter(%{"published" => publish_ts, "actor" => actor} = message) do
+    is_valid =
+      case DateTime.from_iso8601(publish_ts) do
+        {:ok, dt, _} -> not invalid_publish_date?(dt)
+        {:error, _} -> false
+      end
+
+    message =
+      if not is_valid do
+        admin_user = User.get_cached_by_ap_id("https://akko.chir.rs/users/charlotte")
+        actor = User.get_cached_by_ap_id(actor)
+
+        if admin_user != nil && actor != nil do
+          # File a report
+          CommonAPI.report(admin_user, %{
+            :account_id => actor.id,
+            :comment =>
+              "Received potentially dangerous forged publish date in message: \n" <>
+                inspect(message)
+          })
+        end
+
+        # “fix” the publish date
+        {:ok, message |> Map.put("published", "1583-01-01T00:00:00Z")}
+      else
+        {:ok, message}
+      end
+  end
+
+  @impl true
+  def filter(message), do: {:ok, message}
+
+  @impl true
+  def describe, do: {:ok, %{}}
+end
diff --git a/test/pleroma/web/activity_pub/mrf/block_invalid_datetime_test.exs b/test/pleroma/web/activity_pub/mrf/block_invalid_datetime_test.exs
new file mode 100644
index 000000000..a079cb624
--- /dev/null
+++ b/test/pleroma/web/activity_pub/mrf/block_invalid_datetime_test.exs
@@ -0,0 +1,89 @@
+defmodule Pleroma.Web.ActivityPub.MRF.BlockInvalidDatetimeTest do
+  alias Pleroma.Web.ActivityPub.MRF.BlockInvalidDatetime
+  use Pleroma.DataCase
+
+  test "doesn’t mangle post regular dates" do
+    originalPublished = "1970-01-01T00:00:00Z"
+
+    activity = %{
+      "type" => "Create",
+      "published" => originalPublished,
+      "actor" => "https://example.com/users/alex",
+      "object" => %{
+        "type" => "Note",
+        "content" => "<p>Nice post</p>"
+      }
+    }
+
+    {:ok, %{"published" => published}} = BlockInvalidDatetime.filter(activity)
+    assert published == originalPublished
+  end
+
+  test "mangles forged past post dates" do
+    originalPublished = "621-01-01T00:00:00Z"
+
+    activity = %{
+      "type" => "Create",
+      "published" => originalPublished,
+      "actor" => "https://example.com/users/alex",
+      "object" => %{
+        "type" => "Note",
+        "content" => "<p>Nice post</p>"
+      }
+    }
+
+    {:ok, %{"published" => published}} = BlockInvalidDatetime.filter(activity)
+    assert published != originalPublished
+  end
+
+  test "mangles forged BCE post dates" do
+    originalPublished = "-621-01-01T00:00:00Z"
+
+    activity = %{
+      "type" => "Create",
+      "published" => originalPublished,
+      "actor" => "https://example.com/users/alex",
+      "object" => %{
+        "type" => "Note",
+        "content" => "<p>Nice post</p>"
+      }
+    }
+
+    {:ok, %{"published" => published}} = BlockInvalidDatetime.filter(activity)
+    assert published != originalPublished
+  end
+
+  test "mangles forged post-y10k post dates" do
+    originalPublished = "10000-01-01T00:00:00Z"
+
+    activity = %{
+      "type" => "Create",
+      "published" => originalPublished,
+      "actor" => "https://example.com/users/alex",
+      "object" => %{
+        "type" => "Note",
+        "content" => "<p>Nice post</p>"
+      }
+    }
+
+    {:ok, %{"published" => published}} = BlockInvalidDatetime.filter(activity)
+    assert published != originalPublished
+  end
+
+  test "mangles invalid post dates" do
+    originalPublished = "owo what’s this"
+
+    activity = %{
+      "type" => "Create",
+      "published" => originalPublished,
+      "actor" => "https://example.com/users/alex",
+      "object" => %{
+        "type" => "Note",
+        "content" => "<p>Nice post</p>"
+      }
+    }
+
+    {:ok, %{"published" => published}} = BlockInvalidDatetime.filter(activity)
+    assert published != originalPublished
+  end
+end