diff --git a/lib/ex_unit/lib/ex_unit/diff.ex b/lib/ex_unit/lib/ex_unit/diff.ex
index c5ffcd8b301..b562b646815 100644
--- a/lib/ex_unit/lib/ex_unit/diff.ex
+++ b/lib/ex_unit/lib/ex_unit/diff.ex
@@ -1162,6 +1162,7 @@ defmodule ExUnit.Diff do
     else
       other
       |> Map.to_list()
+      |> Enum.map(&escape_pair/1)
       |> build_map_or_struct(struct)
     end
   end
diff --git a/lib/ex_unit/test/ex_unit/diff_test.exs b/lib/ex_unit/test/ex_unit/diff_test.exs
index 39e69c143e7..2d7c9ab80df 100644
--- a/lib/ex_unit/test/ex_unit/diff_test.exs
+++ b/lib/ex_unit/test/ex_unit/diff_test.exs
@@ -335,6 +335,8 @@ defmodule ExUnit.DiffTest do
       "[[[[], \"Hello-,- \"] | \"world\"] | \"!\"]",
       "[[[[], \"Hello \"] | \"world\"] | \"!\"]"
     )
+
+    refute_diff(:foo = %{bar: [:a | :b]}, "", "")
   end
 
   test "proper lists" do
diff --git a/lib/ex_unit/test/ex_unit/formatter_test.exs b/lib/ex_unit/test/ex_unit/formatter_test.exs
index 3e02fd13af7..62ecfc0d2a4 100644
--- a/lib/ex_unit/test/ex_unit/formatter_test.exs
+++ b/lib/ex_unit/test/ex_unit/formatter_test.exs
@@ -510,6 +510,17 @@ defmodule ExUnit.FormatterTest do
            """
   end
 
+  test "formats assertions with nested improper list diffing" do
+    failure = [{:error, catch_assertion(assert :foo = %{bar: [1 | 2]}), []}]
+
+    assert format_test_all_failure(test_module(), failure, 1, :infinity, &diff_formatter/2) =~ """
+           match (=) failed
+                code:  assert :foo = %{bar: [1 | 2]}
+                left:  :foo
+                right: %{bar: [1 | 2]}
+           """
+  end
+
   defmodule BadInspect do
     defstruct key: 0