diff --git a/ocaml-cppo.spec b/ocaml-cppo.spec
index f984037..8e0182d 100644
--- a/ocaml-cppo.spec
+++ b/ocaml-cppo.spec
@@ -31,6 +31,7 @@ BuildRequires:  ocaml-ocamldoc
 BuildRequires:  ocaml-rpm-macros >= 4.03
 BuildRequires:  ocamlfind(easy-format)
 BuildRequires:  ocamlfind(ocamlbuild)
+BuildRequires:  ocamlfind(str)
 BuildRequires:  ocamlfind(unix)
 BuildRoot:      %{_tmppath}/%{name}-%{version}-build
 # ocaml autodep start for pkg: ocaml-cppo
@@ -83,7 +84,7 @@ Library ocamlbuild_cppo
   Path: ocamlbuild_plugin
   Modules: Ocamlbuild_cppo
   Install: true
-  BuildDepends: ocamlbuild
+  BuildDepends: ocamlbuild, str
 
 Document ocamlbuild_cppo
   Title:                API reference for ocamlbuild_cppo