diff --git a/gnu/usr.bin/binutils/as/Makefile.inc0 b/gnu/usr.bin/binutils/as/Makefile.inc0
index 25317854e07..cdcd466861b 100644
--- a/gnu/usr.bin/binutils/as/Makefile.inc0
+++ b/gnu/usr.bin/binutils/as/Makefile.inc0
@@ -25,3 +25,15 @@ LDADD+=		-L${RELTOP}/libopcodes -lopcodes
 DPADD+=		${RELTOP}/libbfd/libbfd.a
 DPADD+=		${RELTOP}/libiberty/libiberty.a
 DPADD+=		${RELTOP}/libopcodes/libopcodes.a
+
+# If set, BINUTILSDISTDIR is the path to a directory containing the full GNU
+# binutils release. FreeBSD only distributes the bits that are required to
+# build native architectures. BINUTILSDISTDIR is needed to build cross tools.
+.if	defined(BINUTILSDISTDIR) && exists(${BINUTILSDISTDIR})
+.PATH:		${BINUTILSDISTDIR}/gas ${BINUTILSDISTDIR}/gas/config
+CFLAGS+=	-I${BINUTILSDISTDIR}/gas
+CFLAGS+=	-I${BINUTILSDISTDIR}/gas/config
+CFLAGS+=	-I${BINUTILSDISTDIR}/bfd
+CFLAGS+=	-I${BINUTILSDISTDIR}/include
+CFLAGS+=	-I${BINUTILSDISTDIR}
+.endif