diff --git a/lib/reline/kill_ring.rb b/lib/reline/kill_ring.rb
index 84d94a7ff6..201f6f3ca0 100644
--- a/lib/reline/kill_ring.rb
+++ b/lib/reline/kill_ring.rb
@@ -68,7 +68,7 @@ class Reline::KillRing
   def append(string, before_p = false)
     case @state
     when State::FRESH, State::YANK
-      @ring << RingPoint.new(string)
+      @ring << RingPoint.new(+string)
       @state = State::CONTINUED
     when State::CONTINUED, State::PROCESSED
       if before_p
diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index b7cc6b747d..5e3a862cc6 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -1256,7 +1256,7 @@ class Reline::LineEditor
         item_mbchars = item.grapheme_clusters
       end
       size = [memo_mbchars.size, item_mbchars.size].min
-      result = ''
+      result = +''
       size.times do |i|
         if @config.completion_ignore_case
           if memo_mbchars[i].casecmp?(item_mbchars[i])
@@ -2935,7 +2935,7 @@ class Reline::LineEditor
   end
 
   private def ed_delete_prev_char(key, arg: 1)
-    deleted = ''
+    deleted = +''
     arg.times do
       if @cursor > 0
         byte_size = Reline::Unicode.get_prev_mbchar_size(@line, @byte_pointer)
diff --git a/lib/reline/windows.rb b/lib/reline/windows.rb
index 6f635f630f..a22331fae5 100644
--- a/lib/reline/windows.rb
+++ b/lib/reline/windows.rb
@@ -85,7 +85,7 @@ class Reline::Windows
       def call(*args)
         import = @proto.split("")
         args.each_with_index do |x, i|
-          args[i], = [x == 0 ? nil : x].pack("p").unpack(POINTER_TYPE) if import[i] == "S"
+          args[i], = [x == 0 ? nil : +x].pack("p").unpack(POINTER_TYPE) if import[i] == "S"
           args[i], = [x].pack("I").unpack("i") if import[i] == "I"
         end
         ret, = @func.call(*args)