diff --git a/lib/irb/init.rb b/lib/irb/init.rb
index 470903b451..4df285ce64 100644
--- a/lib/irb/init.rb
+++ b/lib/irb/init.rb
@@ -76,7 +76,7 @@ module IRB # :nodoc:
     @CONF[:USE_SINGLELINE] = false unless defined?(ReadlineInputMethod)
     @CONF[:USE_COLORIZE] = (nc = ENV['NO_COLOR']).nil? || nc.empty?
     @CONF[:USE_AUTOCOMPLETE] = ENV.fetch("IRB_USE_AUTOCOMPLETE", "true") != "false"
-    @CONF[:COMPLETOR] = :regexp
+    @CONF[:COMPLETOR] = ENV.fetch("IRB_COMPLETOR", "regexp").to_sym
     @CONF[:INSPECT_MODE] = true
     @CONF[:USE_TRACER] = false
     @CONF[:USE_LOADER] = false
diff --git a/test/irb/test_init.rb b/test/irb/test_init.rb
index e330cc5e84..b6a8f5529b 100644
--- a/test/irb/test_init.rb
+++ b/test/irb/test_init.rb
@@ -120,6 +120,34 @@ module TestIRB
       IRB.conf[:USE_AUTOCOMPLETE] = orig_use_autocomplete_conf
     end
 
+    def test_completor_environment_variable
+      orig_use_autocomplete_env = ENV['IRB_COMPLETOR']
+      orig_use_autocomplete_conf = IRB.conf[:COMPLETOR]
+
+      ENV['IRB_COMPLETOR'] = nil
+      IRB.setup(__FILE__)
+      assert_equal(:regexp, IRB.conf[:COMPLETOR])
+
+      ENV['IRB_COMPLETOR'] = 'regexp'
+      IRB.setup(__FILE__)
+      assert_equal(:regexp, IRB.conf[:COMPLETOR])
+
+      ENV['IRB_COMPLETOR'] = 'type'
+      IRB.setup(__FILE__)
+      assert_equal(:type, IRB.conf[:COMPLETOR])
+
+      ENV['IRB_COMPLETOR'] = 'regexp'
+      IRB.setup(__FILE__, argv: ['--type-completor'])
+      assert_equal :type, IRB.conf[:COMPLETOR]
+
+      ENV['IRB_COMPLETOR'] = 'type'
+      IRB.setup(__FILE__, argv: ['--regexp-completor'])
+      assert_equal :regexp, IRB.conf[:COMPLETOR]
+    ensure
+      ENV['IRB_COMPLETOR'] = orig_use_autocomplete_env
+      IRB.conf[:COMPLETOR] = orig_use_autocomplete_conf
+    end
+
     def test_completor_setup_with_argv
       orig_completor_conf = IRB.conf[:COMPLETOR]