diff --git a/lib/review/epubmaker.rb b/lib/review/epubmaker.rb
index 4579e291e..9daf4e134 100644
--- a/lib/review/epubmaker.rb
+++ b/lib/review/epubmaker.rb
@@ -1,4 +1,4 @@
-# Copyright (c) 2010-2023 Kenshi Muto and Masayoshi Takahashi
+# Copyright (c) 2010-2024 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
 # You can distribute or modify this program under the terms of
@@ -523,7 +523,7 @@ def copy_stylesheet(basetmpdir)
     end
 
     def copy_static_file(configname, destdir, destfilename: nil)
-      destfilename ||= @config[configname]
+      destfilename ||= File.basename(@config[configname])
       unless File.exist?(@config[configname])
         error! "#{configname}: #{@config[configname]} is not found."
       end
diff --git a/lib/review/epubmaker/epubcommon.rb b/lib/review/epubmaker/epubcommon.rb
index ec29649af..b2e6cdf6d 100644
--- a/lib/review/epubmaker/epubcommon.rb
+++ b/lib/review/epubmaker/epubcommon.rb
@@ -1,6 +1,6 @@
 # = epubcommon.rb -- super class for EPUBv2 and EPUBv3
 #
-# Copyright (c) 2010-2023 Kenshi Muto and Masayoshi Takahashi
+# Copyright (c) 2010-2024 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
 # You can distribute or modify this program under the terms of
@@ -320,19 +320,19 @@ def flat_ncx(type, indent = nil)
       end
 
       def produce_write_common(basedir, tmpdir)
-        File.write("#{tmpdir}/mimetype", mimetype)
+        File.write(File.join(tmpdir, 'mimetype'), mimetype)
 
-        FileUtils.mkdir_p("#{tmpdir}/META-INF")
-        File.write("#{tmpdir}/META-INF/container.xml", container)
+        FileUtils.mkdir_p(File.join(tmpdir, 'META-INF'))
+        File.write(File.join(tmpdir, 'META-INF', 'container.xml'), container)
 
-        FileUtils.mkdir_p("#{tmpdir}/OEBPS")
+        FileUtils.mkdir_p(File.join(tmpdir, 'OEBPS'))
         File.write(File.join(tmpdir, opf_path), opf)
 
         if config['cover']
-          if File.exist?("#{basedir}/#{config['cover']}")
-            FileUtils.cp("#{basedir}/#{config['cover']}", "#{tmpdir}/OEBPS")
+          if File.exist?(File.join(basedir, File.basename(config['cover'])))
+            FileUtils.cp(File.join(basedir, File.basename(config['cover'])), File.join(tmpdir, 'OEBPS'))
           else
-            File.write("#{tmpdir}/OEBPS/#{config['cover']}", cover)
+            File.write(File.join(tmpdir, 'OEBPS', File.basename(config['cover'])), cover)
           end
         end
 
@@ -344,13 +344,13 @@ def produce_write_common(basedir, tmpdir)
         contents.each do |item|
           next if /#/.match?(item.file) # skip subgroup
 
-          fname = "#{basedir}/#{item.file}"
+          fname = File.join(basedir, item.file)
           unless File.exist?(fname)
             raise ApplicationError, "#{fname} is not found."
           end
 
-          FileUtils.mkdir_p(File.dirname("#{tmpdir}/OEBPS/#{item.file}"))
-          FileUtils.cp(fname, "#{tmpdir}/OEBPS/#{item.file}")
+          FileUtils.mkdir_p(File.dirname(File.join(tmpdir, 'OEBPS', item.file)))
+          FileUtils.cp(fname, File.join(tmpdir, 'OEBPS', item.file))
         end
       end
 
diff --git a/lib/review/pdfmaker.rb b/lib/review/pdfmaker.rb
index a41c7c062..0c480fa51 100644
--- a/lib/review/pdfmaker.rb
+++ b/lib/review/pdfmaker.rb
@@ -1,4 +1,4 @@
-# Copyright (c) 2010-2023 Kenshi Muto and Masayoshi Takahashi
+# Copyright (c) 2010-2024 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
 # You can distribute or modify this program under the terms of
@@ -339,6 +339,7 @@ def make_custom_page(file)
         File.read(file_sty)
       else
         warn "File #{file_sty} is not found."
+        nil
       end
     end
 
@@ -505,6 +506,15 @@ def template_content
         template_dir = @basedir
         template_path = 'layouts/layout.tex.erb'
       end
+
+      if @config['cover'] && !File.exist?(@config['cover'])
+        error! "File #{@config['cover']} is not found."
+      end
+
+      if @config['titlepage'] && @config['titlefile'] && !File.exist?(@config['titlefile'])
+        error! "File #{@config['titlefile']} is not found."
+      end
+
       ReVIEW::Template.generate(path: template_path, mode: '-', binding: binding, template_dir: template_dir)
     rescue StandardError => e
       if defined?(e.full_message)
diff --git a/review.gemspec b/review.gemspec
index 5e8fdaf1a..0dbe77e4d 100644
--- a/review.gemspec
+++ b/review.gemspec
@@ -26,7 +26,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency('rouge')
   gem.add_dependency('rubyzip')
   gem.add_dependency('tty-logger')
-  gem.add_development_dependency('mini_magick')
+  gem.add_development_dependency('mini_magick', '~> 5.0.0')
   gem.add_development_dependency('playwright-runner')
   gem.add_development_dependency('pygments.rb')
   gem.add_development_dependency('rake')
diff --git a/test/test_epubmaker.rb b/test/test_epubmaker.rb
index 0380fbb05..cdca5f825 100644
--- a/test/test_epubmaker.rb
+++ b/test/test_epubmaker.rb
@@ -875,6 +875,9 @@ def error(s)
       File.write(File.join(tmpdir, 'exist.css'), 'body {}')
       File.write(File.join(tmpdir, 'exist.html'), '<html></html>')
 
+      Dir.mkdir(File.join(tmpdir, 'subdir'))
+      File.write(File.join(tmpdir, 'subdir', 'exist.html'), '<html></html>')
+
       Dir.chdir(tmpdir) do
         Dir.mkdir('test')
         yield(epubmaker, File.join(tmpdir, 'test'))
@@ -897,6 +900,9 @@ def test_copy_static_file
       epubmaker.config['titlefile'] = 'exist.html'
       assert_nothing_raised { epubmaker.copy_frontmatter(tmpdir) }
 
+      epubmaker.config['titlefile'] = 'subdir/exist.html'
+      assert_nothing_raised { epubmaker.copy_frontmatter(tmpdir) }
+
       epubmaker.config['titlefile'] = 'nothing.html'
       @log_io.string = ''
       assert_raise(SystemExit) { epubmaker.copy_frontmatter(tmpdir) }
@@ -909,6 +915,9 @@ def test_copy_static_file
         epubmaker.config[name] = 'exist.html'
         assert_nothing_raised { epubmaker.copy_frontmatter(tmpdir) }
 
+        epubmaker.config[name] = 'subdir/exist.html'
+        assert_nothing_raised { epubmaker.copy_frontmatter(tmpdir) }
+
         epubmaker.config[name] = 'nothing.html'
         @log_io.string = ''
         assert_raise(SystemExit) { epubmaker.copy_frontmatter(tmpdir) }
@@ -921,6 +930,9 @@ def test_copy_static_file
         epubmaker.config[name] = 'exist.html'
         assert_nothing_raised { epubmaker.copy_backmatter(tmpdir) }
 
+        epubmaker.config[name] = 'subdir/exist.html'
+        assert_nothing_raised { epubmaker.copy_backmatter(tmpdir) }
+
         epubmaker.config[name] = 'nothing.html'
         @log_io.string = ''
         assert_raise(SystemExit) { epubmaker.copy_backmatter(tmpdir) }
diff --git a/test/test_img_math.rb b/test/test_img_math.rb
index 8f1e49716..33f7d347c 100644
--- a/test/test_img_math.rb
+++ b/test/test_img_math.rb
@@ -87,7 +87,8 @@ def test_make_math_image
   private
 
   def compare_images(image1, image2)
-    compare = MiniMagick::Tool::Compare.new(whiny: false)
+    MiniMagick.errors = false
+    compare = MiniMagick::Tool::Compare.new
     compare << '-fuzz'
     compare << '10%'
     compare.metric('AE')