diff --git a/Makefile.inc1 b/Makefile.inc1
index 5bbc81d932d3..6657f3967139 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -2514,10 +2514,25 @@ CDBENV=MAKEOBJDIRPREFIX=${MAKEOBJDIRPREFIX}/${XDDIR} \
 	INSTALL="sh ${.CURDIR}/tools/install.sh"
 CDENV= ${CDBENV} \
 	TOOLS_PREFIX=${XDTP}
-CD2CFLAGS=-isystem ${XDDESTDIR}/usr/include -L${XDDESTDIR}/usr/lib \
-	--sysroot=${XDDESTDIR}/ -B${XDDESTDIR}/usr/libexec \
-	-B${XDDESTDIR}/usr/bin -B${XDDESTDIR}/usr/lib
-CD2ENV=${CDENV} CC="${CC} ${CD2CFLAGS}" CXX="${CXX} ${CD2CFLAGS}" \
+
+.if ${WANT_COMPILER_TYPE} == gcc || \
+    (defined(X_COMPILER_TYPE) && ${X_COMPILER_TYPE} == gcc)
+# GCC requires -isystem and -L when using a cross-compiler.  --sysroot
+# won't set header path and -L is used to ensure the base library path
+# is added before the port PREFIX library path.
+CD2CFLAGS+=	-isystem ${XDDESTDIR}/usr/include -L${XDDESTDIR}/usr/lib
+# GCC requires -B to find /usr/lib/crti.o when using a cross-compiler
+# combined with --sysroot.
+CD2CFLAGS+=	-B${XDDESTDIR}/usr/lib
+# Force using libc++ for external GCC.
+# XXX: This should be checking MK_GNUCXX == no
+.if ${X_COMPILER_VERSION} >= 40800
+CD2CXXFLAGS+=	-isystem ${XDDESTDIR}/usr/include/c++/v1 -std=c++11 \
+		-nostdinc++
+.endif
+.endif
+CD2CFLAGS+=	--sysroot=${XDDESTDIR}/
+CD2ENV=${CDENV} CC="${CC} ${CD2CFLAGS}" CXX="${CXX} ${CD2CXXFLAGS} ${CD2CFLAGS}" \
 	CPP="${CPP} ${CD2CFLAGS}" \
 	MACHINE=${TARGET} MACHINE_ARCH=${TARGET_ARCH}