diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 870b89b550..4e5860ceb9 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -1158,8 +1158,25 @@ class Reline::LineEditor
 
   def call_completion_proc
     result = retrieve_completion_block(true)
-    slice = result[1]
-    result = @completion_proc.(slice) if @completion_proc and slice
+    preposing, target, postposing = result
+    if @completion_proc and target
+      argnum = @completion_proc.parameters.inject(0) { |result, item|
+        case item.first
+        when :req, :opt
+          result + 1
+        when :rest
+          break 3
+        end
+      }
+      case argnum
+      when 1
+        result = @completion_proc.(target)
+      when 2
+        result = @completion_proc.(target, preposing)
+      when 3..Float::INFINITY
+        result = @completion_proc.(target, preposing, postposing)
+      end
+    end
     Reline.core.instance_variable_set(:@completion_quote_character, nil)
     result
   end
@@ -1264,6 +1281,19 @@ class Reline::LineEditor
       end
       target = before
     end
+    if @is_multiline
+      if @previous_line_index
+        lines = whole_lines(index: @previous_line_index, line: @line)
+      else
+        lines = whole_lines
+      end
+      if @line_index > 0
+        preposing = lines[0..(@line_index - 1)].join("\n") + "\n" + preposing
+      end
+      if (lines.size - 1) > @line_index
+        postposing = postposing + "\n" + lines[(@line_index + 1)..-1].join("\n")
+      end
+    end
     [preposing.encode(@encoding), target.encode(@encoding), postposing.encode(@encoding)]
   end
 
diff --git a/test/reline/test_string_processing.rb b/test/reline/test_string_processing.rb
index e76fa384f2..0e0ee9cc04 100644
--- a/test/reline/test_string_processing.rb
+++ b/test/reline/test_string_processing.rb
@@ -20,4 +20,58 @@ class Reline::LineEditor::StringProcessingTest < Reline::TestCase
     width = @line_editor.send(:calculate_width, "\1\e[31m\2RubyColor\1\e[34m\2 default string \1\e[m\2>", true)
     assert_equal('RubyColor default string >'.size, width)
   end
+
+  def test_completion_proc_with_preposing_and_postposing
+    buf = ['def hoge', '  puts :aaa', 'end']
+
+    @line_editor.instance_variable_set(:@is_multiline, true)
+    @line_editor.instance_variable_set(:@buffer_of_lines, buf)
+    @line_editor.instance_variable_set(:@line, buf[1])
+    @line_editor.instance_variable_set(:@byte_pointer, 3)
+    @line_editor.instance_variable_set(:@cursor, 3)
+    @line_editor.instance_variable_set(:@cursor_max, 11)
+    @line_editor.instance_variable_set(:@line_index, 1)
+    @line_editor.instance_variable_set(:@completion_proc, proc { |target|
+      assert_equal('p', target)
+    })
+    @line_editor.__send__(:call_completion_proc)
+
+    @line_editor.instance_variable_set(:@is_multiline, true)
+    @line_editor.instance_variable_set(:@buffer_of_lines, buf)
+    @line_editor.instance_variable_set(:@line, buf[1])
+    @line_editor.instance_variable_set(:@byte_pointer, 6)
+    @line_editor.instance_variable_set(:@cursor, 6)
+    @line_editor.instance_variable_set(:@cursor_max, 11)
+    @line_editor.instance_variable_set(:@line_index, 1)
+    @line_editor.instance_variable_set(:@completion_proc, proc { |target, pre, post|
+      assert_equal('puts', target)
+      assert_equal("def hoge\n  ", pre)
+      assert_equal(" :aaa\nend", post)
+    })
+    @line_editor.__send__(:call_completion_proc)
+
+    @line_editor.instance_variable_set(:@line, buf[0])
+    @line_editor.instance_variable_set(:@byte_pointer, 6)
+    @line_editor.instance_variable_set(:@cursor, 6)
+    @line_editor.instance_variable_set(:@cursor_max, 8)
+    @line_editor.instance_variable_set(:@line_index, 0)
+    @line_editor.instance_variable_set(:@completion_proc, proc { |target, pre, post|
+      assert_equal('ho', target)
+      assert_equal('def ', pre)
+      assert_equal("ge\n  puts :aaa\nend", post)
+    })
+    @line_editor.__send__(:call_completion_proc)
+
+    @line_editor.instance_variable_set(:@line, buf[2])
+    @line_editor.instance_variable_set(:@byte_pointer, 1)
+    @line_editor.instance_variable_set(:@cursor, 1)
+    @line_editor.instance_variable_set(:@cursor_max, 3)
+    @line_editor.instance_variable_set(:@line_index, 2)
+    @line_editor.instance_variable_set(:@completion_proc, proc { |target, pre, post|
+      assert_equal('e', target)
+      assert_equal("def hoge\n  puts :aaa\n", pre)
+      assert_equal('nd', post)
+    })
+    @line_editor.__send__(:call_completion_proc)
+  end
 end