diff --git a/science/openmc/Makefile b/science/openmc/Makefile
index 40968e6beedc..33a890944bd3 100644
--- a/science/openmc/Makefile
+++ b/science/openmc/Makefile
@@ -1,47 +1,51 @@
 PORTNAME=	openmc
 DISTVERSIONPREFIX=	v
 DISTVERSION=	0.15.0
 CATEGORIES=	science
 
 MAINTAINER=	yuri@FreeBSD.org
 COMMENT=	Monte Carlo neutron and photon transport simulation code
 WWW=		https://openmc.org/
 
 LICENSE=	MIT
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
 BUILD_DEPENDS=	xtensor>0:math/xtensor
 LIB_DEPENDS=	libfmt.so:devel/libfmt \
 		libhdf5.so:science/hdf5 \
 		libpng16.so:graphics/png \
 		libpugixml.so:textproc/pugixml
 
 USES=		cmake:noninja,testing eigen:3 pkgconfig
 
 USE_GITHUB=	yes
 GH_ACCOUNT=	${PORTNAME}-dev
 GH_TUPLE=	catchorg:Catch2:5a40b22:catch2/vendor/Catch2 \
 		martinmoene:gsl-lite:913e86d:gsl_lite/vendor/gsl-lite # gsl-lite isn't ported yet
 
 CMAKE_OFF=	OPENMC_BUILD_TESTS
 CMAKE_TESTING_ON=	OPENMC_BUILD_TESTS # tests are broken, see https://github.com/openmc-dev/openmc/issues/2449
 
 BINARY_ALIAS=	git=false
 
 OPTIONS_DEFINE=		LIBMESH MPI OPENMP
-OPTIONS_DEFAULT=	MPI OPENMP
+OPTIONS_DEFAULT=	MPI
 
 LIBMESH_DESC=		Support for libMesh unstructured mesh tallies
 LIBMESH_CMAKE_BOOL=	OPENMC_USE_LIBMESH
 LIBMESH_LIB_DEPENDS=	libmesh_opt.so:math/libmesh
 
 MPI_VARS=		CXX=${LOCALBASE}/bin/mpic++ # compilation breaks with OpenMPI-{3,4} and LIBMESH=ON
 MPI_BUILD_DEPENDS=	mpich>0:net/mpich
 MPI_RUN_DEPENDS=	mpich>0:net/mpich
 
 OPENMP_CMAKE_BOOL=	OPENMC_USE_OPENMP
 
+.if exists(/usr/include/omp.h)
+OPTIONS_DEFAULT+=	OPENMP
+.endif
+
 post-install:
 	${RM} -r ${STAGEDIR}${DOCSDIR}
 
 .include <bsd.port.mk>