diff --git a/lib/rubygems/installer.rb b/lib/rubygems/installer.rb
index b5644c36b7..1e35e4fe83 100644
--- a/lib/rubygems/installer.rb
+++ b/lib/rubygems/installer.rb
@@ -226,7 +226,8 @@ class Gem::Installer
       line = io.gets
       shebang = /^#!.*ruby/
 
-      if load_relative_enabled?
+      # TruffleRuby uses a bash prelude in default launchers
+      if load_relative_enabled? || RUBY_ENGINE == "truffleruby"
         until line.nil? || line =~ shebang do
           line = io.gets
         end