diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c3bb75015..7d4659154 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -46,6 +46,7 @@ jobs:
           - "3.1"
           - ruby-head
           - jruby-9.3
+          - truffleruby-head
     steps:
       - uses: actions/checkout@v1
       - name: Set up Ruby
diff --git a/spec/prawn_manual_spec.rb b/spec/prawn_manual_spec.rb
index 57720ccd0..5db18f035 100644
--- a/spec/prawn_manual_spec.rb
+++ b/spec/prawn_manual_spec.rb
@@ -4,12 +4,11 @@
 require 'digest/sha2'
 
 MANUAL_HASH =
-  case RUBY_ENGINE
-  when 'ruby'
-    '1dbd5d466eb58d4d495aee6869eb839e3995fbe8607318c491786b959f490e5aab968574a2fea8c3e42ef3d54374bc903357f5cc7b5065f5fe71999830d7c995'
-  when 'jruby'
-    'e23a8336dd55ca007d93eaaacb9ef6ca4d3e91d4b6ccf5e504925212907ebf3a0c7334e1a614ee5e54de800bd4500a3b2430e038bd9f75879c4a69c68589408d'
-  end
+  {
+    'ruby' => '1dbd5d466eb58d4d495aee6869eb839e3995fbe8607318c491786b959f490e5aab968574a2fea8c3e42ef3d54374bc903357f5cc7b5065f5fe71999830d7c995',
+    'jruby' => 'e23a8336dd55ca007d93eaaacb9ef6ca4d3e91d4b6ccf5e504925212907ebf3a0c7334e1a614ee5e54de800bd4500a3b2430e038bd9f75879c4a69c68589408d',
+    'truffleruby' => '2d001a18e27582cce60a6610ca0239de96e7413b0c2a657af5ef364cdc793f3ecd22fbf0ca88bd33cbc24f08cbf0f055cc24a9c2661087047b8ddd14c4554fa5'
+  }.freeze
 
 RSpec.describe Prawn do
   describe 'manual' do
@@ -27,7 +26,7 @@
 
       hash = Digest::SHA512.hexdigest(s)
 
-      expect(hash).to eq MANUAL_HASH
+      expect(hash).to eq MANUAL_HASH[RUBY_ENGINE]
     end
   end
 end