diff --git a/src/main/java/org/jruby/ext/openssl/X509Cert.java b/src/main/java/org/jruby/ext/openssl/X509Cert.java
index ec1f96c4..5289f36a 100644
--- a/src/main/java/org/jruby/ext/openssl/X509Cert.java
+++ b/src/main/java/org/jruby/ext/openssl/X509Cert.java
@@ -555,7 +555,7 @@ public IRubyObject sign(final ThreadContext context, final IRubyObject key, fina
         for ( X509Extension ext : uniqueExtensions() ) {
             try {
                 final byte[] bytes = ext.getRealValueEncoded();
-                builder.addExtension(ext.getRealObjectID(), ext.isRealCritical(), bytes);
+                builder.addExtension(ext.getRealObjectID().getId(), ext.isRealCritical(), bytes);
             }
             catch (IOException ioe) {
                 throw runtime.newIOErrorFromException(ioe);