diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index d1b3b31646451044a7ffc6dcc1880b4bc7ac0d68..ccdf2c30409da63fe2676c8c80e6b7d470d452fb 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,22 @@
+*   `truncate` would return the original string if it was too short to be truncated
+    and a frozen string if it were long enough to be truncated. Now truncate will
+    consistently return an unfrozen string regardless. This behavior is consistent
+    with `gsub` and `strip`.
 
+    Before:
+
+      'foobar'.truncate(5).frozen?
+      => true
+      'foobar'.truncate(6).frozen?
+      => false
+
+    After:
+
+      'foobar'.truncate(5).frozen?
+      => false
+      'foobar'.truncate(6).frozen?
+      => false
+
+    *Jordan Thomas*
 
 Please check [6-0-stable](https://github.com/rails/rails/blob/6-0-stable/activesupport/CHANGELOG.md) for previous changes.
diff --git a/activesupport/lib/active_support/core_ext/string/filters.rb b/activesupport/lib/active_support/core_ext/string/filters.rb
index df0e79afa8ed488e1fefe9bf2d561a6a4f7149ef..7f28bd52f244a2b9292b3b727488d9967b151fbd 100644
--- a/activesupport/lib/active_support/core_ext/string/filters.rb
+++ b/activesupport/lib/active_support/core_ext/string/filters.rb
@@ -75,7 +75,7 @@ def truncate(truncate_at, options = {})
         length_with_room_for_omission
       end
 
-    "#{self[0, stop]}#{omission}"
+    +"#{self[0, stop]}#{omission}"
   end
 
   # Truncates +text+ to at most <tt>bytesize</tt> bytes in length without
diff --git a/activesupport/test/core_ext/string_ext_test.rb b/activesupport/test/core_ext/string_ext_test.rb
index 4ffa33aa612d51b418f3947baa178628edd0b729..c5a000b67ab02c8cf79f4af25ba0943bfa9108f8 100644
--- a/activesupport/test/core_ext/string_ext_test.rb
+++ b/activesupport/test/core_ext/string_ext_test.rb
@@ -291,6 +291,11 @@ def test_truncate_with_omission_and_regexp_separator
     assert_equal "Hello Big[...]", "Hello Big World!".truncate(15, omission: "[...]", separator: /\s/)
   end
 
+  def test_truncate_returns_frozen_string
+    assert_not "Hello World!".truncate(12).frozen?
+    assert_not "Hello World!!".truncate(12).frozen?
+  end
+
   def test_truncate_bytes
     assert_equal "👍👍👍👍", "👍👍👍👍".truncate_bytes(16)
     assert_equal "👍👍👍👍", "👍👍👍👍".truncate_bytes(16, omission: nil)