diff --git a/ext/json/ext/parser/parser.c b/ext/json/ext/parser/parser.c
index 876bec57..095dd99e 100644
--- a/ext/json/ext/parser/parser.c
+++ b/ext/json/ext/parser/parser.c
@@ -587,7 +587,7 @@ cs = 0;
         if (json->allow_nan) {
             *result = CInfinity;
         } else {
-            rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 8);
+            rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 7);
         }
     }
 	goto st29;
diff --git a/ext/json/ext/parser/parser.rl b/ext/json/ext/parser/parser.rl
index 1ecf3317..2602d91f 100644
--- a/ext/json/ext/parser/parser.rl
+++ b/ext/json/ext/parser/parser.rl
@@ -229,7 +229,7 @@ static char *JSON_parse_object(JSON_Parser *json, char *p, char *pe, VALUE *resu
         if (json->allow_nan) {
             *result = CInfinity;
         } else {
-            rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 8);
+            rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 7);
         }
     }
     action parse_string {
diff --git a/tests/json_ext_parser_test.rb b/tests/json_ext_parser_test.rb
index b5b18fb2..f49f88b5 100644
--- a/tests/json_ext_parser_test.rb
+++ b/tests/json_ext_parser_test.rb
@@ -3,6 +3,8 @@
 
 class JSONExtParserTest < Test::Unit::TestCase
   if defined?(JSON::Ext::Parser)
+    include JSON
+
     def test_allocate
       parser = JSON::Ext::Parser.new("{}")
       assert_raise(TypeError, '[ruby-core:35079]') do
@@ -11,5 +13,22 @@ def test_allocate
       parser = JSON::Ext::Parser.allocate
       assert_raise(TypeError, '[ruby-core:35079]') { parser.source }
     end
+
+    def test_error_messages
+      ex = assert_raise(ParserError) { parse('Infinity') }
+      assert_equal "unexpected token at 'Infinity'", ex.message
+
+      unless RUBY_PLATFORM =~ /java/
+        ex = assert_raise(ParserError) { parse('-Infinity') }
+        assert_equal "unexpected token at '-Infinity'", ex.message
+      end
+
+      ex = assert_raise(ParserError) { parse('NaN') }
+      assert_equal "unexpected token at 'NaN'", ex.message
+    end
+
+    def parse(json)
+      JSON::Ext::Parser.new(json).parse
+    end
   end
 end