diff --git a/lib/elixir/lib/module/types/descr.ex b/lib/elixir/lib/module/types/descr.ex
index 772e63e85db..7c765af9230 100644
--- a/lib/elixir/lib/module/types/descr.ex
+++ b/lib/elixir/lib/module/types/descr.ex
@@ -2260,6 +2260,11 @@ defmodule Module.Types.Descr do
 
   defp map_only?(descr), do: empty?(Map.delete(descr, :map))
 
+  def map_normal_form([{tag, pos, negs}], acc), do: [{tag, acc ++ pos, negs}]
+
+  def map_normal_form([{tag1, pos1, negs1}, {tag2, pos2, negs2} | rest]) do
+  end
+
   defp map_union(dnf1, dnf2) do
     # Union is just concatenation, but we rely on some optimization strategies to
     # avoid the list to grow when possible
@@ -2370,6 +2375,8 @@ defmodule Module.Types.Descr do
     if subtype?(v2, v1), do: :right_subtype_of_left
   end
 
+  defp map_intersection(dnf, dnf), do: dnf
+
   # Given two unions of maps, intersects each pair of maps.
   defp map_intersection(dnf1, dnf2) do
     for {tag1, pos1, negs1} <- dnf1,
@@ -2378,15 +2385,17 @@ defmodule Module.Types.Descr do
       acc ->
         try do
           {tag, fields} = map_literal_intersection(tag1, pos1, tag2, pos2)
-          entry = {tag, fields, negs1 ++ negs2}
+          negs = negs1 ++ (negs2 -- negs1)
+          entry = {tag, fields, negs}
 
           # Imagine a, b, c, where a is closed and b and c are open with
           # no keys in common. The result in both cases will be a and we
           # want to avoid adding duplicates, especially as intersection
           # is a cartesian product.
-          case :lists.member(entry, acc) do
-            true -> acc
-            false -> [entry | acc]
+          cond do
+            :lists.member({tag, fields}, negs) -> acc
+            :lists.member(entry, acc) -> acc
+            true -> [entry | acc]
           end
         catch
           :empty -> acc
@@ -2454,33 +2463,42 @@ defmodule Module.Types.Descr do
     if empty?(type), do: throw(:empty), else: type
   end
 
-  defp map_difference(_, dnf) when dnf == @map_top do
-    0
-  end
+  defp map_difference(_, dnf) when dnf == @map_top, do: 0
+  defp map_difference(dnf, dnf), do: 0
 
   defp map_difference(dnf1, dnf2) do
     Enum.reduce(dnf2, dnf1, fn
-      # Optimization: we are removing an open map with one field.
-      {:open, fields2, []}, dnf1 when map_size(fields2) == 1 ->
-        Enum.reduce(dnf1, [], fn {tag1, fields1, negs1}, acc ->
+      {:open, fields2, []}, current_dnf when map_size(fields2) == 1 ->
+        # Optimization: we are removing an open map with one field.
+        Enum.reduce(current_dnf, [], fn {tag1, fields1, negs1}, acc ->
           {key, value, _rest} = :maps.next(:maps.iterator(fields2))
           t_diff = difference(Map.get(fields1, key, tag_to_type(tag1)), value)
 
           if empty?(t_diff) do
             acc
           else
-            [{tag1, Map.put(fields1, key, t_diff), negs1} | acc]
+            {tag, pos} = {tag1, Map.put(fields1, key, t_diff)}
+
+            cond do
+              :lists.member({tag, pos}, negs1) -> acc
+              true -> [{tag, pos, negs1} | acc]
+            end
           end
         end)
 
-      {tag2, fields2, negs2}, dnf1 ->
-        Enum.reduce(dnf1, [], fn {tag1, fields1, negs1}, acc ->
-          acc = [{tag1, fields1, [{tag2, fields2} | negs1]} | acc]
+      {tag2, fields2, negs2}, current_dnf ->
+        Enum.reduce(current_dnf, [], fn {tag1, fields1, negs1}, acc ->
+          negs = [{tag2, fields2} | negs1]
+          acc = [{tag1, fields1, negs} | acc]
 
           Enum.reduce(negs2, acc, fn {neg_tag2, neg_fields2}, acc ->
             try do
               {tag, fields} = map_literal_intersection(tag1, fields1, neg_tag2, neg_fields2)
-              [{tag, fields, negs1} | acc]
+
+              cond do
+                :lists.member({tag, fields}, negs1) -> acc
+                true -> [{tag, fields, negs1} | acc]
+              end
             catch
               :empty -> acc
             end
diff --git a/lib/elixir/lib/module/types/helpers.ex b/lib/elixir/lib/module/types/helpers.ex
index aea8c0b6074..2795f9d1090 100644
--- a/lib/elixir/lib/module/types/helpers.ex
+++ b/lib/elixir/lib/module/types/helpers.ex
@@ -495,4 +495,101 @@ defmodule Module.Types.Helpers do
   defp zip_map_reduce([], [], list, acc, _fun) do
     {Enum.reverse(list), acc}
   end
+
+  def descr_size(:term), do: 1
+
+  def descr_size(%{} = descr) do
+    Enum.reduce(descr, 0, fn {key, value}, acc ->
+      acc + descr_size(key, value)
+    end)
+  end
+
+  def descr_size(list) when is_list(list) do
+    dnf_size(list)
+  end
+
+  def dnf_size(dnf) do
+    Enum.reduce(dnf, 0, fn {_tag, pos, negs}, acc ->
+      negs_size =
+        Enum.reduce(negs, 0, fn {_neg_tag, fields}, neg_acc ->
+          neg_acc + 1 + map_size(fields)
+        end)
+
+      acc + 1 + map_size(pos) + negs_size
+    end)
+  end
+
+  def dnf_size_detailed(dnf) do
+    {total_pos, total_negs} =
+      Enum.reduce(dnf, {0, 0}, fn {_tag, pos, negs}, {pos_acc, neg_acc} ->
+        negs_size =
+          Enum.reduce(negs, 0, fn {_neg_tag, fields}, neg_sum ->
+            neg_sum + 1 + map_size(fields)
+          end)
+
+        {pos_acc + map_size(pos), neg_acc + negs_size}
+      end)
+
+    {total_pos, total_negs}
+  end
+
+  def descr_size(:tuple, dnf), do: length(dnf)
+  def descr_size(:fun, bdd), do: bdd_size(bdd)
+
+  def descr_size(:map, dnf) do
+    Enum.reduce(dnf, 0, fn {_tag, _pos, negs}, acc ->
+      acc + 1 + length(negs)
+    end)
+  end
+
+  def descr_size(:list, dnf) do
+    Enum.reduce(dnf, 0, fn {_, _last, negs}, acc ->
+      acc + 1 + length(negs)
+    end)
+  end
+
+  def descr_size(_, _), do: 1
+
+  def bdd_size({_fun, l, r}) do
+    bdd_size(l) + bdd_size(r) + 1
+  end
+
+  def bdd_size(_bdd), do: 0
+
+  def list_dnf_size(dnf) do
+    Enum.reduce(dnf, 0, fn {_, _, negs}, _acc ->
+      1 + length(negs)
+    end)
+  end
+
+  # defp map_difference_check_sizes(dnf1, dnf2) do
+  #   {pos1, neg1} = Module.Types.Helpers.dnf_size_detailed(dnf1)
+  #   {pos2, neg2} = Module.Types.Helpers.dnf_size_detailed(dnf2)
+  #   IO.inspect({length(dnf1), pos1, neg1}, label: "dnf1 (clauses, pos, neg)")
+  #   IO.inspect({length(dnf2), pos2, neg2}, label: "dnf2 (clauses, pos, neg)")
+
+  #   IO.puts("dnf1 breakdown:")
+
+  #   Enum.with_index(dnf1, fn {tag, pos, negs}, idx ->
+  #     negs_size =
+  #       Enum.reduce(negs, 0, fn {_neg_tag, fields}, acc ->
+  #         acc + 1 + map_size(fields)
+  #       end)
+
+  #     IO.inspect({idx, tag, map_size(pos), negs_size}, label: "  clause")
+  #     IO.puts(Module.Types.Descr.to_quoted_string(%{map: [{tag, pos, negs}]}))
+  #   end)
+
+  #   IO.puts("dnf2 breakdown:")
+
+  #   Enum.with_index(dnf2, fn {tag, pos, negs}, idx ->
+  #     negs_size =
+  #       Enum.reduce(negs, 0, fn {_neg_tag, fields}, acc ->
+  #         acc + 1 + map_size(fields)
+  #       end)
+
+  #     IO.inspect({idx, tag, map_size(pos), negs_size}, label: "  clause")
+  #     IO.puts(Module.Types.Descr.to_quoted_string(%{map: [{tag, pos, negs}]}))
+  #   end)
+  # end
 end