diff --git a/CHANGELOG.md b/CHANGELOG.md
index 136f8f3..5734b72 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ The format is loosely based on [Keep a Changelog][keepachangelog], and this
 project adheres to [Semantic Versioning][semver].
 
 ## Unreleased
+- fixed: Handle datetime serialization format via `:datetime_type` config.
 
 ## v0.17.1
 - changed: Bump minimum ecto to `3.12`.
diff --git a/lib/ecto/adapters/sqlite3/codec.ex b/lib/ecto/adapters/sqlite3/codec.ex
index 3cd5375..61df7d7 100644
--- a/lib/ecto/adapters/sqlite3/codec.ex
+++ b/lib/ecto/adapters/sqlite3/codec.ex
@@ -114,12 +114,16 @@ defmodule Ecto.Adapters.SQLite3.Codec do
   end
 
   @text_datetime_format "%Y-%m-%d %H:%M:%S"
+  @iso8601_format "%Y-%m-%dT%H:%M:%S"
+
+  def datetime_format(:text_datetime), do: @text_datetime_format
+  def datetime_format(_), do: @iso8601_format
 
   def utc_datetime_encode(nil, :iso8601), do: {:ok, nil}
   def utc_datetime_encode(nil, :text_datetime), do: {:ok, nil}
 
   def utc_datetime_encode(%{time_zone: "Etc/UTC"} = value, :iso8601) do
-    {:ok, NaiveDateTime.to_iso8601(value)}
+    {:ok, Calendar.strftime(value, @iso8601_format)}
   end
 
   def utc_datetime_encode(%{time_zone: "Etc/UTC"} = value, :text_datetime) do
@@ -135,7 +139,7 @@ defmodule Ecto.Adapters.SQLite3.Codec do
   def naive_datetime_encode(nil, :text_datetime), do: {:ok, nil}
 
   def naive_datetime_encode(value, :iso8601) do
-    {:ok, NaiveDateTime.to_iso8601(value)}
+    {:ok, Calendar.strftime(value, @iso8601_format)}
   end
 
   def naive_datetime_encode(value, :text_datetime) do
diff --git a/lib/ecto/adapters/sqlite3/connection.ex b/lib/ecto/adapters/sqlite3/connection.ex
index 790d1c7..e0a6760 100644
--- a/lib/ecto/adapters/sqlite3/connection.ex
+++ b/lib/ecto/adapters/sqlite3/connection.ex
@@ -1369,10 +1369,14 @@ defmodule Ecto.Adapters.SQLite3.Connection do
     [quote_name(name)]
   end
 
+  @datetime_type Application.compile_env(:ecto_sqlite3, :datetime_type, :iso8601)
+
   defp expr({:datetime_add, _, [datetime, count, interval]}, sources, query) do
+    format = Ecto.Adapters.SQLite3.Codec.datetime_format(@datetime_type)
+
     [
       "CAST (",
-      "strftime('%Y-%m-%d %H:%M:%f000Z'",
+      "strftime('#{format}'",
       ",",
       expr(datetime, sources, query),
       ",",
diff --git a/test/ecto/adapters/sqlite3/connection/datetime_add_test.exs b/test/ecto/adapters/sqlite3/connection/datetime_add_test.exs
index 9fd62dc..583ab8a 100644
--- a/test/ecto/adapters/sqlite3/connection/datetime_add_test.exs
+++ b/test/ecto/adapters/sqlite3/connection/datetime_add_test.exs
@@ -11,7 +11,7 @@ defmodule Ecto.Adapters.SQLite3.Connection.DatetimeAddTest do
       |> select([], true)
       |> plan()
 
-    assert ~s{SELECT 1 FROM "schema" AS s0 WHERE (CAST (strftime('%Y-%m-%d %H:%M:%f000Z',s0.\"foo\",1 || ' month') AS TEXT) > s0."bar")} ==
+    assert ~s{SELECT 1 FROM "schema" AS s0 WHERE (CAST (strftime('%Y-%m-%dT%H:%M:%S',s0.\"foo\",1 || ' month') AS TEXT) > s0."bar")} ==
              all(query)
   end
 
@@ -22,7 +22,7 @@ defmodule Ecto.Adapters.SQLite3.Connection.DatetimeAddTest do
       |> select([], true)
       |> plan()
 
-    assert ~s{SELECT 1 FROM "schema" AS s0 WHERE (CAST (strftime('%Y-%m-%d %H:%M:%f000Z',CAST(s0.\"foo\" AS TEXT),1 || ' month') AS TEXT) > s0."bar")} ==
+    assert ~s{SELECT 1 FROM "schema" AS s0 WHERE (CAST (strftime('%Y-%m-%dT%H:%M:%S',CAST(s0.\"foo\" AS TEXT),1 || ' month') AS TEXT) > s0."bar")} ==
              all(query)
   end
 end
diff --git a/test/ecto/integration/timestamps_test.exs b/test/ecto/integration/timestamps_test.exs
index 00b1362..1ea3e6c 100644
--- a/test/ecto/integration/timestamps_test.exs
+++ b/test/ecto/integration/timestamps_test.exs
@@ -181,6 +181,31 @@ defmodule Ecto.Integration.TimestampsTest do
              |> TestRepo.all()
   end
 
+  test "using built in ecto functions" do
+    account = insert_account(%{name: "Test"})
+
+    insert_product(%{
+      account_id: account.id,
+      name: "Foo",
+      inserted_at: seconds_ago(1)
+    })
+
+    insert_product(%{
+      account_id: account.id,
+      name: "Bar",
+      inserted_at: seconds_ago(3)
+    })
+
+    assert [
+             %{name: "Foo"},
+           ] =
+             Product
+             |> select([p], p)
+             |> where([p], p.inserted_at >= ago(2, "second"))
+             |> order_by([p], desc: p.inserted_at)
+             |> TestRepo.all()
+  end
+
   defp insert_account(attrs) do
     %Account{}
     |> Account.changeset(attrs)
@@ -192,4 +217,9 @@ defmodule Ecto.Integration.TimestampsTest do
     |> Product.changeset(attrs)
     |> TestRepo.insert!()
   end
+
+  defp seconds_ago(seconds) do
+    now = DateTime.utc_now()
+    DateTime.add(now, -seconds, :second)
+  end
 end