diff --git a/lib/ecto/adapters/myxql/connection.ex b/lib/ecto/adapters/myxql/connection.ex
index c3c45359..33440908 100644
--- a/lib/ecto/adapters/myxql/connection.ex
+++ b/lib/ecto/adapters/myxql/connection.ex
@@ -950,6 +950,9 @@ if Code.ensure_loaded?(MyXQL) do
     defp op_to_binary({:not, _, [_]} = expr, sources, query),
       do: paren_expr(expr, sources, query)
 
+    defp op_to_binary({:in, _, [_, _]} = expr, sources, query),
+      do: paren_expr(expr, sources, query)
+
     defp op_to_binary(expr, sources, query),
       do: expr(expr, sources, query)
 
diff --git a/lib/ecto/adapters/postgres/connection.ex b/lib/ecto/adapters/postgres/connection.ex
index a8d7d5c1..96bf5820 100644
--- a/lib/ecto/adapters/postgres/connection.ex
+++ b/lib/ecto/adapters/postgres/connection.ex
@@ -1215,6 +1215,9 @@ if Code.ensure_loaded?(Postgrex) do
     defp maybe_paren({:not, _, [_]} = expr, sources, query),
       do: paren_expr(expr, sources, query)
 
+    defp maybe_paren({:in, _, [_, _]} = expr, sources, query),
+      do: paren_expr(expr, sources, query)
+
     defp maybe_paren(expr, sources, query),
       do: expr(expr, sources, query)
 
diff --git a/test/ecto/adapters/myxql_test.exs b/test/ecto/adapters/myxql_test.exs
index 373bb6e4..ed5a809e 100644
--- a/test/ecto/adapters/myxql_test.exs
+++ b/test/ecto/adapters/myxql_test.exs
@@ -854,7 +854,13 @@ defmodule Ecto.Adapters.MyXQLTest do
     query = Schema |> select([e], e.x == ^0 or e.x in ^[1, 2, 3] or e.x == ^4) |> plan()
 
     assert all(query) ==
-             ~s{SELECT ((s0.`x` = ?) OR s0.`x` IN (?,?,?)) OR (s0.`x` = ?) FROM `schema` AS s0}
+             ~s{SELECT ((s0.`x` = ?) OR (s0.`x` IN (?,?,?))) OR (s0.`x` = ?) FROM `schema` AS s0}
+
+    query = "schema" |> select([e], e.x in [1, 2] in [true]) |> plan()
+    assert all(query) == ~s{SELECT (s0.`x` IN (1,2)) IN (TRUE) FROM `schema` AS s0}
+
+    query = "schema" |> select([e], e.x in ^[1, 2] in [true]) |> plan()
+    assert all(query) == ~s{SELECT (s0.`x` IN (?,?)) IN (TRUE) FROM `schema` AS s0}
   end
 
   test "in subquery" do
diff --git a/test/ecto/adapters/postgres_test.exs b/test/ecto/adapters/postgres_test.exs
index deb551f9..00ac5159 100644
--- a/test/ecto/adapters/postgres_test.exs
+++ b/test/ecto/adapters/postgres_test.exs
@@ -1123,7 +1123,7 @@ defmodule Ecto.Adapters.PostgresTest do
     query = Schema |> select([e], e.x == ^0 or e.x in ^[1, 2, 3] or e.x == ^4) |> plan()
 
     assert all(query) ==
-             ~s{SELECT ((s0."x" = $1) OR s0."x" = ANY($2)) OR (s0."x" = $3) FROM "schema" AS s0}
+             ~s{SELECT ((s0."x" = $1) OR (s0."x" = ANY($2))) OR (s0."x" = $3) FROM "schema" AS s0}
 
     query = "schema" |> select([e], (not e.x) in [true, false]) |> plan()
     assert all(query) == ~s{SELECT (NOT (s0."x")) IN (TRUE,FALSE) FROM "schema" AS s0}
@@ -1133,6 +1133,15 @@ defmodule Ecto.Adapters.PostgresTest do
 
     query = "schema" |> select([e], (not e.x) in e.w) |> plan()
     assert all(query) == ~s{SELECT (NOT (s0."x")) = ANY(s0."w") FROM "schema" AS s0}
+
+    query = "schema" |> select([e], e.x == e.y in ^[1, 2]) |> plan()
+    assert all(query) == ~s{SELECT s0."x" = (s0."y" = ANY($1)) FROM "schema" AS s0}
+
+    query = "schema" |> select([e], e.x == e.y in e.w) |> plan()
+    assert all(query) == ~s{SELECT s0."x" = (s0."y" = ANY(s0."w")) FROM "schema" AS s0}
+
+    query = "schema" |> select([e], e.x in [1, 2] in [true]) |> plan()
+    assert all(query) == ~s{SELECT (s0."x" IN (1,2)) IN (TRUE) FROM "schema" AS s0}
   end
 
   test "in subquery" do