2 files changed, 26 insertions, 13 deletions
diff --git a/activesupport/lib/active_support/core_ext/object/duplicable.rb b/activesupport/lib/active_support/core_ext/object/duplicable.rb
index ea81df2bd8..c27fd4f792 100644
--- a/activesupport/lib/active_support/core_ext/object/duplicable.rb
+++ b/activesupport/lib/active_support/core_ext/object/duplicable.rb
@@ -124,21 +124,31 @@ class Method
 end
 
 class Complex
-  # Complexes are not duplicable:
-  #
-  # Complex(1).duplicable? # => false
-  # Complex(1).dup         # => TypeError: can't copy Complex
-  def duplicable?
-    false
+  begin
+    Complex(1).dup
+  rescue TypeError
+
+    # Complexes are not duplicable for RUBY_VERSION < 2.5.0:
+    #
+    # Complex(1).duplicable? # => false
+    # Complex(1).dup         # => TypeError: can't copy Complex
+    def duplicable?
+      false
+    end
   end
 end
 
 class Rational
-  # Rationals are not duplicable:
-  #
-  # Rational(1).duplicable? # => false
-  # Rational(1).dup         # => TypeError: can't copy Rational
-  def duplicable?
-    false
+  begin
+    Rational(1).dup
+  rescue TypeError
+
+    # Rationals are not duplicable for RUBY_VERSION < 2.5.0:
+    #
+    # Rational(1).duplicable? # => false
+    # Rational(1).dup         # => TypeError: can't copy Rational
+    def duplicable?
+      false
+    end
   end
 end
diff --git a/activesupport/test/core_ext/object/duplicable_test.rb b/activesupport/test/core_ext/object/duplicable_test.rb
index e6f3c8aef2..68b0129980 100644
--- a/activesupport/test/core_ext/object/duplicable_test.rb
+++ b/activesupport/test/core_ext/object/duplicable_test.rb
@@ -4,7 +4,10 @@ require "active_support/core_ext/object/duplicable"
 require "active_support/core_ext/numeric/time"
 
 class DuplicableTest < ActiveSupport::TestCase
-  if RUBY_VERSION >= "2.4.1"
+  if RUBY_VERSION >= "2.5.0"
+    RAISE_DUP = [method(:puts)]
+    ALLOW_DUP = ["1", "symbol_from_string".to_sym, Object.new, /foo/, [], {}, Time.now, Class.new, Module.new, BigDecimal.new("4.56"), nil, false, true, 1, 2.3, Complex(1), Rational(1)]
+  elsif RUBY_VERSION >= "2.4.1"
     RAISE_DUP = [method(:puts), Complex(1), Rational(1)]
     ALLOW_DUP = ["1", "symbol_from_string".to_sym, Object.new, /foo/, [], {}, Time.now, Class.new, Module.new, BigDecimal.new("4.56"), nil, false, true, 1, 2.3]
   elsif RUBY_VERSION >= "2.4.0"  # Due to 2.4.0 bug. This elsif cannot be removed unless we drop 2.4.0 support...