diff --git a/ext/openssl/ossl_hmac.c b/ext/openssl/ossl_hmac.c
index 757754cd9..efbf558b6 100644
--- a/ext/openssl/ossl_hmac.c
+++ b/ext/openssl/ossl_hmac.c
@@ -94,9 +94,9 @@ ossl_hmac_alloc(VALUE klass)
  *  instance == other_instance
  *  #=> false
  *
- * Use #digest and compare in constant time:
+ * Instead, compare in constant time:
  *
- *	OpenSSL.fixed_length_secure_compare(instance.digest, other_instance.digest)
+ *	OpenSSL.fixed_length_secure_compare(instance, other_instance)
  *	#=> true
  *
  */
diff --git a/lib/openssl.rb b/lib/openssl.rb
index ec143bc74..be2969557 100644
--- a/lib/openssl.rb
+++ b/lib/openssl.rb
@@ -17,6 +17,7 @@
 require_relative 'openssl/cipher'
 require_relative 'openssl/config'
 require_relative 'openssl/digest'
+require_relative 'openssl/hmac'
 require_relative 'openssl/x509'
 require_relative 'openssl/ssl'
 require_relative 'openssl/pkcs5'
diff --git a/lib/openssl/hmac.rb b/lib/openssl/hmac.rb
new file mode 100644
index 000000000..d974aa3f7
--- /dev/null
+++ b/lib/openssl/hmac.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module OpenSSL
+  class HMAC
+    def to_str
+      digest
+    end
+  end
+end
diff --git a/test/test_hmac.rb b/test/test_hmac.rb
index 831a5b6b3..66d4f385e 100644
--- a/test/test_hmac.rb
+++ b/test/test_hmac.rb
@@ -39,6 +39,14 @@ def test_reset_keep_key
     second = h1.update("test").hexdigest
     assert_equal first, second
   end
+
+  def test_to_str
+    h1 = OpenSSL::HMAC.new("KEY", "SHA1")
+    assert_equal h1.digest, h1.to_str
+
+    h2 = OpenSSL::HMAC.new("KEY", "SHA1")
+    assert_equal h1.to_str, h2.to_str
+  end
 end
 
 end