diff --git a/lib/optparse.rb b/lib/optparse.rb
index e1069b3..9cbd377 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -7,6 +7,7 @@
 #
 # See OptionParser for documentation.
 #
+require 'set' unless defined?(Set)
 
 #--
 # == Developer Documentation (not for RDoc output)
@@ -1500,7 +1501,7 @@ def make_switch(opts, block = nil)
       case o
       when Proc, Method
         block = notwice(o, block, 'block')
-      when Array, Hash
+      when Array, Hash, Set
         if Array === o
           o, v = o.partition {|v,| Completion.completable?(v)}
           values = notwice(v, values, 'values') unless v.empty?
diff --git a/test/optparse/test_switch.rb b/test/optparse/test_switch.rb
new file mode 100644
index 0000000..b06f4e3
--- /dev/null
+++ b/test/optparse/test_switch.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: false
+
+require 'test/unit'
+require 'optparse'
+
+
+class TestOptionParserSwitch < Test::Unit::TestCase
+
+  def setup
+    @parser = OptionParser.new
+  end
+
+  def assert_invalidarg_error(msg, &block)
+    exc = assert_raise(OptionParser::InvalidArgument) do
+      yield
+    end
+    assert_equal "invalid argument: #{msg}", exc.message
+  end
+
+  def test_make_switch__enum_array
+    p = @parser
+    p.on("--enum=<val>", ["aa", "bb", "cc"])
+    p.permute(["--enum=bb"], into: (opts={}))
+    assert_equal({:enum=>"bb"}, opts)
+    assert_invalidarg_error("--enum=dd") do
+      p.permute(["--enum=dd"], into: (opts={}))
+    end
+  end
+
+  def test_make_switch__enum_hash
+    p = @parser
+    p.on("--hash=<val>", {"aa"=>"AA", "bb"=>"BB"})
+    p.permute(["--hash=bb"], into: (opts={}))
+    assert_equal({:hash=>"BB"}, opts)
+    assert_invalidarg_error("--hash=dd") do
+      p.permute(["--hash=dd"], into: (opts={}))
+    end
+  end
+
+  def test_make_switch__enum_set
+    p = @parser
+    p.on("--set=<val>", Set.new(["aa", "bb", "cc"]))
+    p.permute(["--set=bb"], into: (opts={}))
+    assert_equal({:set=>"bb"}, opts)
+    assert_invalidarg_error("--set=dd") do
+      p.permute(["--set=dd"], into: (opts={}))
+    end
+  end
+
+end