diff --git a/dev-ml/ppx_tools/ppx_tools-6.3.ebuild b/dev-ml/ppx_tools/ppx_tools-6.3.ebuild
index b8a168bdfde7c..fa8079b62de12 100644
--- a/dev-ml/ppx_tools/ppx_tools-6.3.ebuild
+++ b/dev-ml/ppx_tools/ppx_tools-6.3.ebuild
@@ -15,3 +15,5 @@ LICENSE="MIT"
 SLOT="0/${PV}"
 KEYWORDS="amd64 ~arm ~arm64 ~ppc ~ppc64 x86"
 IUSE="+ocamlopt"
+
+BDEPEND="dev-ml/cppo"
diff --git a/dev-ml/ppx_tools/ppx_tools-6.4.ebuild b/dev-ml/ppx_tools/ppx_tools-6.4.ebuild
index 1d025b5dacda5..b8c31373448b3 100644
--- a/dev-ml/ppx_tools/ppx_tools-6.4.ebuild
+++ b/dev-ml/ppx_tools/ppx_tools-6.4.ebuild
@@ -15,3 +15,5 @@ LICENSE="MIT"
 SLOT="0/${PV}"
 KEYWORDS="~amd64 ~arm ~arm64 ~ppc ~ppc64 ~x86"
 IUSE="+ocamlopt"
+
+BDEPEND="dev-ml/cppo"