diff --git a/lib/fluent/time.rb b/lib/fluent/time.rb
index 52eed0b1f5..eba7a186fa 100644
--- a/lib/fluent/time.rb
+++ b/lib/fluent/time.rb
@@ -292,7 +292,7 @@ def initialize(type, localtime = nil, timezone = nil)
 
     def parse_unixtime(value)
       unless value.is_a?(String) || value.is_a?(Numeric)
-        raise TimeParseError, "value must be a string or a number: #{value}(value.class)"
+        raise TimeParseError, "value must be a string or a number: #{value}(#{value.class})"
       end
 
       if @cache1_key == value
@@ -323,7 +323,7 @@ def parse_unixtime(value)
     ## parse_by_to_r  (msec): 28.232856 sec
     def parse_float(value)
       unless value.is_a?(String) || value.is_a?(Numeric)
-        raise TimeParseError, "value must be a string or a number: #{value}(value.class)"
+        raise TimeParseError, "value must be a string or a number: #{value}(#{value.class})"
       end
 
       if @cache1_key == value