diff --git a/cad/horizon-eda/Makefile b/cad/horizon-eda/Makefile
index a09a1df10c92..32b9f386943f 100644
--- a/cad/horizon-eda/Makefile
+++ b/cad/horizon-eda/Makefile
@@ -23,7 +23,7 @@ LIB_DEPENDS=	libcurl.so:ftp/curl \
 		libzip.so:archivers/libzip \
 		libzmq.so:net/libzmq4
 
-USES=		compiler:c++17-lang gmake gnome libarchive localbase pkgconfig python:build sqlite
+USES=		gmake gnome libarchive localbase pkgconfig python:build sqlite # compiler:c++17-lang
 USE_GNOME=	atkmm gdkpixbuf2 gtkmm30 librsvg2
 
 USE_GITHUB=	yes
@@ -33,6 +33,12 @@ MAKE_ARGS=	DEBUGFLAGS= OPTIMIZE=
 
 BINARY_ALIAS=	python3=${PYTHON_CMD}
 
+LLVM_VER=	12 # workaround for bug#263870
+BUILD_DEPENDS+=	clang${LLVM_VER}:devel/llvm${LLVM_VER}
+CPP=		clang-cpp${LLVM_VER}
+CC=		clang${LLVM_VER}
+CXX=		clang++${LLVM_VER}
+
 post-install: # https://github.com/horizon-eda/horizon/issues/558
 	@cd ${STAGEDIR}${PREFIX}/bin && ${STRIP_CMD} horizon-eda horizon-imp