diff --git a/lib/irb/completion.rb b/lib/irb/completion.rb
index 3795cea43..e3137bc36 100644
--- a/lib/irb/completion.rb
+++ b/lib/irb/completion.rb
@@ -107,7 +107,14 @@ def completion_candidates(preposing, target, _postposing, bind:)
 
       return commands unless result
 
-      commands | result.completion_candidates.map { target + _1 }
+      encoded_candidates = result.completion_candidates.filter_map do |i|
+        encoded = i.encode(Encoding.default_external)
+        target + encoded
+      rescue Encoding::UndefinedConversionError
+        # If the string cannot be converted, we just ignore it
+        nil
+      end
+      commands | encoded_candidates
     end
 
     def doc_namespace(preposing, matched, _postposing, bind:)
@@ -194,7 +201,12 @@ def completion_candidates(preposing, target, postposing, bind:)
       # It doesn't make sense to propose commands with other preposing
       commands = [] unless preposing.empty?
 
-      completion_data = retrieve_completion_data(target, bind: bind, doc_namespace: false).compact.map{ |i| i.encode(Encoding.default_external) }
+      completion_data = retrieve_completion_data(target, bind: bind, doc_namespace: false).compact.filter_map do |i|
+        i.encode(Encoding.default_external)
+      rescue Encoding::UndefinedConversionError
+        # If the string cannot be converted, we just ignore it
+        nil
+      end
       commands | completion_data
     end
 
diff --git a/test/irb/test_completion.rb b/test/irb/test_completion.rb
index c9a0eafa3..3bdf920da 100644
--- a/test/irb/test_completion.rb
+++ b/test/irb/test_completion.rb
@@ -314,4 +314,34 @@ def test_retrieve_completion_data
       assert_equal(IRB::InputCompletor.retrieve_completion_data('a.abs', bind: bind, doc_namespace: true), 'Integer.abs')
     end
   end
+
+  class InvalidEncodingMethodTest < TestCase
+    def test_regexp_completor_handles_encoding_errors_gracefully
+      if RUBY_ENGINE == 'truffleruby'
+        omit "TruffleRuby does not support invalid encoding methods."
+      end
+
+      invalid_method_name = "b\xff".force_encoding(Encoding::ASCII_8BIT)
+
+      test_obj = Object.new
+      test_obj.define_singleton_method(invalid_method_name) {}
+      test_bind = test_obj.instance_eval { binding }
+
+      original_encoding = Encoding.default_external
+
+      begin
+        Encoding.default_external = Encoding::UTF_8
+
+        completor = IRB::RegexpCompletor.new
+
+        assert_nothing_raised do
+          result = completor.completion_candidates('', 'b', '', bind: test_bind)
+          assert_include(result, 'block_given?')
+          assert_not_include(result, nil)
+        end
+      ensure
+        Encoding.default_external = original_encoding
+      end
+    end
+  end
 end
diff --git a/test/irb/test_type_completor.rb b/test/irb/test_type_completor.rb
index 3d0e25d19..6389bf1f6 100644
--- a/test/irb/test_type_completor.rb
+++ b/test/irb/test_type_completor.rb
@@ -80,6 +80,28 @@ def test_command_completion
       assert_include(@completor.completion_candidates('', 'show_s', '', bind: binding), 'show_source')
       assert_not_include(@completor.completion_candidates(';', 'show_s', '', bind: binding), 'show_source')
     end
+
+    def test_type_completor_handles_encoding_errors_gracefully
+      invalid_method_name = "b\xff".dup.force_encoding(Encoding::ASCII_8BIT)
+
+      test_obj = Object.new
+      test_obj.define_singleton_method(invalid_method_name) {}
+      test_bind = test_obj.instance_eval { binding }
+
+      original_encoding = Encoding.default_external
+
+      begin
+        Encoding.default_external = Encoding::UTF_8
+
+        assert_nothing_raised do
+          result = @completor.completion_candidates('', 'b', '', bind: test_bind)
+          assert_include(result, 'block_given?')
+          assert_not_include(result, nil)
+        end
+      ensure
+        Encoding.default_external = original_encoding
+      end
+    end
   end
 
   class TypeCompletorIntegrationTest < IntegrationTestCase