diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 86fc4d9bba..a37c9d8508 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -405,7 +405,10 @@ class Reline::LineEditor
 
   private def complete_internal_proc(list, is_menu)
     preposing, target, postposing = @retrieve_completion_block.(@line, @byte_pointer)
-    list = list.select { |i| i&.start_with?(target) }
+    list = list.select { |i|
+      raise Encoding::CompatibilityError if i and i.encoding != @encoding
+      i&.start_with?(target)
+    }
     if is_menu
       menu(target, list)
       return nil
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index 04afff34d9..535906ea24 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -4,8 +4,9 @@ class Reline::KeyActor::Emacs::Test < Reline::TestCase
   def setup
     @prompt = '> '
     @config = Reline::Config.new # Emacs mode is default
+    @encoding = (RELINE_TEST_ENCODING rescue Encoding.default_external)
     @line_editor = Reline::LineEditor.new(@config)
-    @line_editor.reset(@prompt, (RELINE_TEST_ENCODING rescue Encoding.default_external))
+    @line_editor.reset(@prompt, @encoding)
     @line_editor.retrieve_completion_block = Reline.method(:retrieve_completion_block)
   end
 
@@ -1054,6 +1055,8 @@ class Reline::KeyActor::Emacs::Test < Reline::TestCase
         foo_bar
         foo_baz
         qux
+      }.map { |i|
+        i.encode(@encoding)
       }
     }
     input_keys('fo')
@@ -1096,6 +1099,8 @@ class Reline::KeyActor::Emacs::Test < Reline::TestCase
         foo_bar
         foo_baz
         qux
+      }.map { |i|
+        i.encode(@encoding)
       }
     }
     input_keys('abcde fo ABCDE')