2 files changed, 13 insertions, 0 deletions
diff --git a/spec/ruby/optional/capi/ext/string_spec.c b/spec/ruby/optional/capi/ext/string_spec.c
index 2bcd3be243..b9a4a55853 100644
--- a/spec/ruby/optional/capi/ext/string_spec.c
+++ b/spec/ruby/optional/capi/ext/string_spec.c
@@ -87,6 +87,10 @@ VALUE string_spec_rb_str_tmp_new_klass(VALUE self, VALUE len) {
   return RBASIC_CLASS(rb_str_tmp_new(NUM2LONG(len)));
 }
 
+VALUE string_spec_rb_str_buf_append(VALUE self, VALUE str, VALUE two) {
+  return rb_str_buf_append(str, two);
+}
+
 VALUE string_spec_rb_str_buf_cat(VALUE self, VALUE str) {
   const char *question_mark = "?";
   rb_str_buf_cat(str, question_mark, strlen(question_mark));
@@ -599,6 +603,7 @@ void Init_string_spec(void) {
   rb_define_method(cls, "rb_str_buf_new2", string_spec_rb_str_buf_new2, 0);
   rb_define_method(cls, "rb_str_tmp_new", string_spec_rb_str_tmp_new, 1);
   rb_define_method(cls, "rb_str_tmp_new_klass", string_spec_rb_str_tmp_new_klass, 1);
+  rb_define_method(cls, "rb_str_buf_append", string_spec_rb_str_buf_append, 2);
   rb_define_method(cls, "rb_str_buf_cat", string_spec_rb_str_buf_cat, 1);
   rb_define_method(cls, "rb_enc_str_buf_cat", string_spec_rb_enc_str_buf_cat, 3);
   rb_define_method(cls, "rb_str_cat", string_spec_rb_str_cat, 1);
diff --git a/spec/ruby/optional/capi/string_spec.rb b/spec/ruby/optional/capi/string_spec.rb
index ce387ffa49..0cf22e0287 100644
--- a/spec/ruby/optional/capi/string_spec.rb
+++ b/spec/ruby/optional/capi/string_spec.rb
@@ -378,6 +378,14 @@ describe "C-API String function" do
     it_behaves_like :string_times, :rb_str_times, -> str, times { @s.rb_str_times(str, times) }
   end
 
+  describe "rb_str_buf_append" do
+    it "concatenates a string to another string" do
+      str = "Your house "
+      @s.rb_str_buf_append(str, "is on fire?").should.equal?(str)
+      str.should == "Your house is on fire?"
+    end
+  end
+
   describe "rb_str_buf_cat" do
     it "concatenates a C string to a ruby string" do
       @s.rb_str_buf_cat("Your house is on fire").should == "Your house is on fire?"