diff --git a/lib/psych/scalar_scanner.rb b/lib/psych/scalar_scanner.rb
index 68e17ecf..c5cb0c1e 100644
--- a/lib/psych/scalar_scanner.rb
+++ b/lib/psych/scalar_scanner.rb
@@ -92,17 +92,19 @@ def tokenize string
           @symbol_cache[string] = class_loader.symbolize(string.sub(/^:/, ''))
         end
       elsif string.match?(/^[-+]?[0-9][0-9_]*(:[0-5]?[0-9]){1,2}$/)
+        sign = string.start_with?('-') ? -1 : 1
         i = 0
-        string.split(':').each_with_index do |n,e|
+        string.delete_prefix('-').delete_prefix('+').split(':').each_with_index do |n,e|
           i += (n.to_i * 60 ** (e - 2).abs)
         end
-        i
+        i * sign
       elsif string.match?(/^[-+]?[0-9][0-9_]*(:[0-5]?[0-9]){1,2}\.[0-9_]*$/)
+        sign = string.start_with?('-') ? -1 : 1
         i = 0
-        string.split(':').each_with_index do |n,e|
+        string.delete_prefix('-').delete_prefix('+').split(':').each_with_index do |n,e|
           i += (n.to_f * 60 ** (e - 2).abs)
         end
-        i
+        i * sign
       elsif string.match?(FLOAT)
         if string.match?(/\A[-+]?\.\Z/)
           string
diff --git a/test/psych/test_scalar_scanner.rb b/test/psych/test_scalar_scanner.rb
index bc6a74ad..fbaa6b26 100644
--- a/test/psych/test_scalar_scanner.rb
+++ b/test/psych/test_scalar_scanner.rb
@@ -105,6 +105,14 @@ def test_scan_sexagesimal_int
       assert_equal 685230, ss.tokenize('190:20:30')
     end
 
+    def test_scan_negative_sexagesimal_int
+      assert_equal(-685230, ss.tokenize('-190:20:30'))
+    end
+
+    def test_scan_negative_sexagesimal_float
+      assert_equal(-685230.15, ss.tokenize('-190:20:30.15'))
+    end
+
     def test_scan_float
       assert_equal 1.2, ss.tokenize('1.2')
     end