diff --git a/lib/logger/formatter.rb b/lib/logger/formatter.rb
index 34e07bc..c634dbf 100644
--- a/lib/logger/formatter.rb
+++ b/lib/logger/formatter.rb
@@ -3,7 +3,7 @@
 class Logger
   # Default formatter for log messages.
   class Formatter
-    Format = "%s, [%s #%d] %5s -- %s: %s\n"
+    Format = "%.1s, [%s #%d] %5s -- %s: %s\n"
     DatetimeFormat = "%Y-%m-%dT%H:%M:%S.%6N"
 
     attr_accessor :datetime_format
@@ -13,8 +13,7 @@ def initialize
     end
 
     def call(severity, time, progname, msg)
-      Format % [severity[0, 1], format_datetime(time), Process.pid, severity, progname,
-        msg2str(msg)]
+      sprintf(Format, severity, format_datetime(time), Process.pid, severity, progname, msg2str(msg))
     end
 
   private
diff --git a/lib/logger/log_device.rb b/lib/logger/log_device.rb
index 8683328..84277a2 100644
--- a/lib/logger/log_device.rb
+++ b/lib/logger/log_device.rb
@@ -79,8 +79,10 @@ def reopen(log = nil)
     def set_dev(log)
       if log.respond_to?(:write) and log.respond_to?(:close)
         @dev = log
-        if log.respond_to?(:path)
-          @filename = log.path
+        if log.respond_to?(:path) and path = log.path
+          if File.exist?(path)
+            @filename = path
+          end
         end
       else
         @dev = open_logfile(log)
diff --git a/lib/logger/version.rb b/lib/logger/version.rb
index 57735f8..f85c72e 100644
--- a/lib/logger/version.rb
+++ b/lib/logger/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 class Logger
-  VERSION = "1.5.2"
+  VERSION = "1.5.3"
 end
diff --git a/logger.gemspec b/logger.gemspec
index ccd4e70..d12db62 100644
--- a/logger.gemspec
+++ b/logger.gemspec
@@ -23,5 +23,4 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "bundler", ">= 0"
   spec.add_development_dependency "rake", ">= 12.3.3"
   spec.add_development_dependency "test-unit"
-  spec.add_development_dependency "rdoc"
 end