diff --git a/lib/jekyll/cleaner.rb b/lib/jekyll/cleaner.rb
index ca8a0ca9..6c89e2bc 100644
--- a/lib/jekyll/cleaner.rb
+++ b/lib/jekyll/cleaner.rb
@@ -13,7 +13,7 @@ module Jekyll
     # Cleans up the site's destination directory
     def cleanup!
       FileUtils.rm_rf(obsolete_files)
-      FileUtils.rm_rf(metadata_file) if !@site.incremental?
+      FileUtils.rm_rf(metadata_file) unless @site.incremental?
     end
 
     private
diff --git a/lib/jekyll/commands/doctor.rb b/lib/jekyll/commands/doctor.rb
index ba98e653..42bb0110 100644
--- a/lib/jekyll/commands/doctor.rb
+++ b/lib/jekyll/commands/doctor.rb
@@ -59,7 +59,7 @@ module Jekyll
         end
 
         def fsnotify_buggy?(site)
-          return true if !Utils::Platforms.osx?
+          return true unless Utils::Platforms.osx?
           if Dir.pwd != `pwd`.strip
             Jekyll.logger.error "  " + <<-STR.strip.gsub(/\n\s+/, "\n  ")
               We have detected that there might be trouble using fsevent on your
diff --git a/lib/jekyll/commands/serve/servlet.rb b/lib/jekyll/commands/serve/servlet.rb
index fa376f61..7930eb61 100644
--- a/lib/jekyll/commands/serve/servlet.rb
+++ b/lib/jekyll/commands/serve/servlet.rb
@@ -52,7 +52,7 @@ module Jekyll
         def set_defaults
           hash_ = @jekyll_opts.fetch("webrick", {}).fetch("headers", {})
           DEFAULTS.each_with_object(@headers = hash_) do |(key, val), hash|
-            hash[key] = val if !hash.key?(key)
+            hash[key] = val unless hash.key?(key)
           end
         end
       end
diff --git a/lib/jekyll/converters/markdown.rb b/lib/jekyll/converters/markdown.rb
index 8e297dca..07675427 100644
--- a/lib/jekyll/converters/markdown.rb
+++ b/lib/jekyll/converters/markdown.rb
@@ -7,7 +7,7 @@ module Jekyll
 
       def setup
         return if @setup
-        if (!@parser = get_processor)
+        unless (@parser = get_processor)
           Jekyll.logger.error "Invalid Markdown processor given:", @config["markdown"]
           Jekyll.logger.info  "", "Custom processors are not loaded in safe mode" if @config["safe"]
           Jekyll.logger.error "", "Available processors are: #{valid_processors.join(", ")}"
diff --git a/lib/jekyll/regenerator.rb b/lib/jekyll/regenerator.rb
index 52ff5178..cd672830 100644
--- a/lib/jekyll/regenerator.rb
+++ b/lib/jekyll/regenerator.rb
@@ -119,7 +119,7 @@ module Jekyll
     def add_dependency(path, dependency)
       return if (metadata[path].nil? || @disabled)
 
-      if !metadata[path]["deps"].include? dependency
+      unless metadata[path]["deps"].include? dependency
         metadata[path]["deps"] << dependency
         add(dependency) unless metadata.include?(dependency)
       end