diff --git a/sys-cluster/portals4/portals4-1.0_alpha1_p20190109-r2.ebuild b/sys-cluster/portals4/portals4-1.0_alpha1_p20190109-r2.ebuild
index 6bc3a17561..de0c956184 100644
--- a/sys-cluster/portals4/portals4-1.0_alpha1_p20190109-r2.ebuild
+++ b/sys-cluster/portals4/portals4-1.0_alpha1_p20190109-r2.ebuild
@@ -8,7 +8,7 @@ DOCS_BUILDER="doxygen"
 DOCS_CONFIG_NAME="doxygen.conf"
 DOCS_DIR="doc"
 
-inherit autotools docs
+inherit autotools docs optfeature
 
 DESCRIPTION="low-level network API for high-performance networking"
 HOMEPAGE="
@@ -112,3 +112,7 @@ src_install() {
 	einstalldocs
 	find "${D}" -name '*.la' -delete || die
 }
+
+pkg_postinst() {
+	optfeature "Required for correctness with the IB transport. Ensure that /dev/ummunotify is readable/writable by the user running the portals software." sys-kernel/ummunotify
+}