diff --git a/lib/ecto/changeset.ex b/lib/ecto/changeset.ex
index cd0daeffe9..9c80eb0eb3 100644
--- a/lib/ecto/changeset.ex
+++ b/lib/ecto/changeset.ex
@@ -538,12 +538,12 @@ defmodule Ecto.Changeset do
         case fetch_change(changeset, field) do
           {:ok, new_value} ->
             case type do
-              {tag, relation} when tag in @relations ->
+              {tag, _relation} when tag in @relations ->
                 if opts != [] do
                   raise ArgumentError, "invalid options for #{tag} field"
                 end
 
-                relation_changed?(relation.cardinality, new_value)
+                true
 
               _ ->
                 Enum.all?(opts, fn
@@ -567,14 +567,6 @@ defmodule Ecto.Changeset do
     end
   end
 
-  defp relation_changed?(:one, changeset) do
-    changeset.action != :update or changeset.changes != %{}
-  end
-
-  defp relation_changed?(:many, changesets) do
-    Enum.any?(changesets, &relation_changed?(:one, &1))
-  end
-
   @doc """
   Returns the default empty values used by `Ecto.Changeset`.
 
diff --git a/test/ecto/changeset/belongs_to_test.exs b/test/ecto/changeset/belongs_to_test.exs
index f62ff36b46..5ee2177d1e 100644
--- a/test/ecto/changeset/belongs_to_test.exs
+++ b/test/ecto/changeset/belongs_to_test.exs
@@ -569,4 +569,31 @@ defmodule Ecto.Changeset.BelongsToTest do
     changeset2 = %{changeset | action: :delete}
     assert Relation.apply_changes(embed, changeset2) == nil
   end
+
+  test "changed?/2 with assocs" do
+    new_profile = %Profile{name: "profile"}
+
+    changeset =
+      %Author{}
+      |> Changeset.change()
+      |> Changeset.put_assoc(:profile, new_profile)
+
+    assert Changeset.changed?(changeset, :profile)
+
+    {:ok, existing_profile} = TestRepo.insert(%Profile{name: "profile"})
+
+    changeset =
+      %Author{}
+      |> Changeset.change()
+      |> Changeset.put_assoc(:profile, existing_profile)
+
+    assert Changeset.changed?(changeset, :profile)
+
+    changeset =
+      %Author{profile: existing_profile}
+      |> Changeset.change()
+      |> Changeset.put_assoc(:profile, nil)
+
+    assert Changeset.changed?(changeset, :profile)
+  end
 end