diff --git a/tool/checksum.rb b/tool/checksum.rb
index 0de54a314d..3b41aedcfc 100755
--- a/tool/checksum.rb
+++ b/tool/checksum.rb
@@ -67,6 +67,6 @@ class Checksum
   def self.update(argv)
     k = new(VPath.new)
     k.source, k.target, *argv = k.def_options.parse(*argv)
-    k.update {|k| yield(k, *argv)}
+    k.update {|_| yield(_, *argv)}
   end
 end
diff --git a/tool/rbinstall.rb b/tool/rbinstall.rb
index 9e935bdb47..5a55b39add 100755
--- a/tool/rbinstall.rb
+++ b/tool/rbinstall.rb
@@ -590,7 +590,7 @@ install?(:local, :comm, :man) do
           STDIN.reopen(f)
           begin
             destfile << suffix
-            IO.popen(compress) {|f| f.read}
+            IO.popen(compress, &:read)
           ensure
             STDIN.reopen(stdin)
             stdin.close
diff --git a/tool/transcode-tblgen.rb b/tool/transcode-tblgen.rb
index 5134a49b43..156b2de197 100644
--- a/tool/transcode-tblgen.rb
+++ b/tool/transcode-tblgen.rb
@@ -145,7 +145,7 @@ class ActionMap
                 else
                   b = $1.to_i(16)
                   e = $2.to_i(16)
-                  b.upto(e) {|c| set[c] = true }
+                  b.upto(e) {|_| set[_] = true }
                 end
               }
               i = nil
@@ -297,10 +297,10 @@ class ActionMap
         raise ArgumentError, "ambiguous pattern: #{prefix}" if min.length != prefix.length
         h[action] = true
       end
-      region_rects.each {|min, max, action|
+      for min, _, action in region_rects
         raise ArgumentError, "ambiguous pattern: #{prefix}" if !min.empty?
         h[action] = true
-      }
+      end
       tree = Action.new(block.call(prefix, h.keys))
       h.clear
     else