diff --git a/ext/fastthread/extconf.rb b/ext/fastthread/extconf.rb
index fcacfd9..479a3d9 100644
--- a/ext/fastthread/extconf.rb
+++ b/ext/fastthread/extconf.rb
@@ -1,3 +1,9 @@
-require 'mkmf'
-
-create_makefile('fastthread')
+if !defined?(RUBY_ENGINE) || RUBY_ENGINE == "ruby"
+  require 'mkmf'
+  
+  create_makefile('fastthread')
+else
+  File.open('Makefile', 'w') do |f|
+    f.puts("all:")
+  end
+end
diff --git a/ext/fastthread/fastthread.c b/ext/fastthread/fastthread.c
index 355ed00..680d9b9 100644
--- a/ext/fastthread/fastthread.c
+++ b/ext/fastthread/fastthread.c
@@ -10,6 +10,8 @@
  */
 
 #include <ruby.h>
+#ifndef RUBY_VM
+
 #include <intern.h>
 #include <rubysig.h>
 
@@ -623,7 +625,7 @@ wait_condvar(ConditionVariable *condvar, Mutex *mutex)
         rb_raise(private_eThreadError, "not owner of the synchronization mutex");
     }
     unlock_mutex_inner(mutex);
-    rb_ensure(wait_list, (VALUE)&condvar->waiting, lock_mutex, (VALUE)mutex);
+    rb_ensure((VALUE (*) (ANYARGS))wait_list, (VALUE)&condvar->waiting, lock_mutex, (VALUE)mutex);
 }
 
 static VALUE
@@ -1169,9 +1171,12 @@ setup_classes(VALUE unused)
     return Qnil;
 }
 
+#endif /* RUBY_VM */
+
 void
 Init_fastthread()
 {
+    #ifndef RUBY_VM
     int saved_critical;
 
     rb_require("thread");
@@ -1182,5 +1187,6 @@ Init_fastthread()
     saved_critical = rb_thread_critical;
     rb_thread_critical = 1;
     rb_ensure(setup_classes, Qnil, set_critical, (VALUE)saved_critical);
+    #endif /* RUBY_VM */
 }
 
diff --git a/setup.rb b/setup.rb
index f54f84e..f259fb5 100755
--- a/setup.rb
+++ b/setup.rb
@@ -1383,11 +1383,15 @@ class Installer
   end
 
   def rubyextentions(dir)
-    ents = glob_select("*.#{@config.dllext}", targetfiles())
-    if ents.empty?
-      setup_rb_error "no ruby extention exists: 'ruby #{$0} setup' first"
+    if !defined?(RUBY_ENGINE) || RUBY_ENGINE == "ruby"
+      ents = glob_select("*.#{@config.dllext}", targetfiles())
+      if ents.empty?
+        setup_rb_error "no ruby extention exists: 'ruby #{$0} setup' first"
+      end
+      ents
+    else
+      []
     end
-    ents
   end
 
   def targetfiles