diff --git a/sys-cluster/sionlib/sionlib-1.7.6-r1.ebuild b/sys-cluster/sionlib/sionlib-1.7.6-r1.ebuild
index 4b83280642..bd43b5fa2d 100644
--- a/sys-cluster/sionlib/sionlib-1.7.6-r1.ebuild
+++ b/sys-cluster/sionlib/sionlib-1.7.6-r1.ebuild
@@ -44,6 +44,11 @@ pkg_setup() {
 	fortran-2_pkg_setup
 }
 
+src_prepare() {
+	default
+	sed 's/CXXFLAGS = $(CXXFLAGS)/CXXFLAGS = /' -i test/serial/Makefile || die
+}
+
 src_configure() {
 	tc-export AR CC CXX F77 FC
 	export MPICC=/usr/bin/mpicc