diff --git a/ChangeLog b/ChangeLog
index 666200de0b709e..6ab1afed51b6ed 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sun Dec 18 12:03:13 2011  Aaron Patterson <aaron@tenderlovemaking.com>
+
+	* ext/psych/lib/psych/scalar_scanner.rb: Strings that look like dates
+	  should be treated as strings and not dates.
+
+	* test/psych/test_scalar_scanner.rb: corresponding tests.
+
 Sun Dec 18 09:43:21 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
 
 	* test/thread/test_queue.rb (test_thr_kill): extend timeout.
diff --git a/ext/psych/lib/psych/scalar_scanner.rb b/ext/psych/lib/psych/scalar_scanner.rb
index a265a2baf3a205..fa2d385a637711 100644
--- a/ext/psych/lib/psych/scalar_scanner.rb
+++ b/ext/psych/lib/psych/scalar_scanner.rb
@@ -46,9 +46,13 @@ def tokenize string
         end
       when TIME
         parse_time string
-      when /^\d{4}-\d{1,2}-\d{1,2}$/
+      when /^\d{4}-(?:1[012]|0\d|\d)-(?:[12]\d|3[01]|0\d|\d)$/
         require 'date'
-        Date.strptime(string, '%Y-%m-%d')
+        begin
+          Date.strptime(string, '%Y-%m-%d')
+        rescue ArgumentError
+          string
+        end
       when /^\.inf$/i
         1 / 0.0
       when /^-\.inf$/i
diff --git a/test/psych/test_scalar_scanner.rb b/test/psych/test_scalar_scanner.rb
index 659909909e6e4b..cf0dfff6aaaf80 100644
--- a/test/psych/test_scalar_scanner.rb
+++ b/test/psych/test_scalar_scanner.rb
@@ -1,4 +1,5 @@
 require 'psych/helper'
+require 'date'
 
 module Psych
   class TestScalarScanner < TestCase
@@ -20,6 +21,27 @@ def test_scan_time
       end
     end
 
+    def test_scan_bad_dates
+      x = '2000-15-01'
+      assert_equal x, @ss.tokenize(x)
+
+      x = '2000-10-51'
+      assert_equal x, @ss.tokenize(x)
+
+      x = '2000-10-32'
+      assert_equal x, @ss.tokenize(x)
+    end
+
+    def test_scan_good_edge_date
+      x = '2000-1-31'
+      assert_equal Date.strptime(x, '%Y-%m-%d'), @ss.tokenize(x)
+    end
+
+    def test_scan_bad_edge_date
+      x = '2000-11-31'
+      assert_equal x, @ss.tokenize(x)
+    end
+
     def test_scan_date
       date = '1980-12-16'
       token = @ss.tokenize date