diff --git a/spec/ruby/optional/capi/class_spec.rb b/spec/ruby/optional/capi/class_spec.rb
index 07e9e42ad1..1486ab6d7f 100644
--- a/spec/ruby/optional/capi/class_spec.rb
+++ b/spec/ruby/optional/capi/class_spec.rb
@@ -149,6 +149,17 @@ describe "C-API Class function" do
     end
   end
 
+  describe "rb_prepend_module" do
+    it "prepends a module into a class" do
+      klass = Class.new
+      mod = Module.new
+
+      @s.rb_prepend_module(klass, mod)
+
+      klass.ancestors[0, 2].should == [mod, klass]
+    end
+  end
+
   describe "rb_define_attr" do
     before :each do
       @a = CApiClassSpecs::Attr.new
diff --git a/spec/ruby/optional/capi/ext/class_spec.c b/spec/ruby/optional/capi/ext/class_spec.c
index 8ac0e7a93f..0722ea5915 100644
--- a/spec/ruby/optional/capi/ext/class_spec.c
+++ b/spec/ruby/optional/capi/ext/class_spec.c
@@ -144,6 +144,11 @@ static VALUE class_spec_include_module(VALUE self, VALUE klass, VALUE module) {
   return klass;
 }
 
+static VALUE class_spec_prepend_module(VALUE self, VALUE klass, VALUE module) {
+  rb_prepend_module(klass, module);
+  return klass;
+}
+
 void Init_class_spec(void) {
   VALUE cls = rb_define_class("CApiClassSpecs", rb_cObject);
   rb_define_method(cls, "define_call_super_method", class_spec_define_call_super_method, 2);
@@ -173,6 +178,7 @@ void Init_class_spec(void) {
   rb_define_method(cls, "rb_define_class_id_under", class_spec_rb_define_class_id_under, 3);
   rb_define_method(cls, "rb_define_class_variable", class_spec_define_class_variable, 3);
   rb_define_method(cls, "rb_include_module", class_spec_include_module, 2);
+  rb_define_method(cls, "rb_prepend_module", class_spec_prepend_module, 2);
 }
 
 #ifdef __cplusplus