diff --git a/ext/psych/lib/psych/scalar_scanner.rb b/ext/psych/lib/psych/scalar_scanner.rb
index 5fafaf30b3..b66ff9938c 100644
--- a/ext/psych/lib/psych/scalar_scanner.rb
+++ b/ext/psych/lib/psych/scalar_scanner.rb
@@ -33,7 +33,7 @@ module Psych
 
       # Check for a String type, being careful not to get caught by hash keys, hex values, and
       # special floats (e.g., -.inf).
-      if string.match?(/^[^\d\.:-]?[A-Za-z_\s!@#\$%\^&\*\(\)\{\}\<\>\|\/\\~;=]+/) || string.match?(/\n/)
+      if string.match?(%r{^[^\d.:-]?[[:alpha:]_\s!@#$%\^&*(){}<>|/\\~;=]+}) || string.match?(/\n/)
         return string if string.length > 5
 
         if string.match?(/^[^ytonf~]/i)
diff --git a/test/psych/test_scalar_scanner.rb b/test/psych/test_scalar_scanner.rb
index cac8b8feb1..abd5515501 100644
--- a/test/psych/test_scalar_scanner.rb
+++ b/test/psych/test_scalar_scanner.rb
@@ -156,5 +156,27 @@ module Psych
     def test_scan_plus_dot
       assert_equal '+.', ss.tokenize('+.')
     end
+
+    class MatchCallCounter < String
+      attr_reader :match_call_count
+
+      def match?(pat)
+        @match_call_count ||= 0
+        @match_call_count += 1
+        super
+      end
+    end
+
+    def test_scan_ascii_matches_quickly
+      ascii = MatchCallCounter.new('abcdefghijklmnopqrstuvwxyz')
+      ss.tokenize(ascii)
+      assert_equal 1, ascii.match_call_count
+    end
+
+    def test_scan_unicode_matches_quickly
+      unicode = MatchCallCounter.new('鳥かご関連用品')
+      ss.tokenize(unicode)
+      assert_equal 1, unicode.match_call_count
+    end
   end
 end