diff --git a/stand/libsa/zfs/Makefile.inc b/stand/libsa/zfs/Makefile.inc
--- a/stand/libsa/zfs/Makefile.inc
+++ b/stand/libsa/zfs/Makefile.inc
@@ -54,18 +54,19 @@
 CFLAGS_EARLY.list.c+= ${ZFS_EARLY}
 CFLAGS_EARLY.zfs_zstd.c+= ${ZFS_EARLY}
 CFLAGS_EARLY.nvlist.c+= ${ZFS_EARLY}
+CFLAGS_EARLY.zfs.c += ${ZFS_EARLY}
 
-# Can't use the early flags because there's two conflicting definitions of boolean_t in
-# the zfs code that need to be unified, as well as a number of other hacks for pre-openzfs
-# code still in the tree that needs to be fixed.
+#
+# zfs.c is special: we need to define HAS_ZSTD_ZFS to get zfssubr.c to initialize zstd
+# properly. We need to have the cddl boot compat directory in the include path for zfssubr.c
+# to be found, and we need a couple of other include paths for skein and lz4. Finally we
+# temporarily need LDRSRC to pick up disk.h until that layering violation is corrected.
+#
 CFLAGS.zfs.c+=	-DHAS_ZSTD_ZFS					\
 		-I${SYSDIR}/cddl/boot/zfs			\
 		-I${LDRSRC}					\
 		-I${SYSDIR}/crypto/skein			\
-		-I${ZFSOSINC}/spl				\
-		-I${SRCTOP}/sys/cddl/contrib/opensolaris/common/lz4 \
-		-I${ZFSOSINC}/zfs				\
-		-I${OZFS}/include
+		-I${SRCTOP}/sys/cddl/contrib/opensolaris/common/lz4
 
 #
 # ZSTD coding style has some issues, so suppress clang's warnings. Also, zstd's
diff --git a/sys/cddl/boot/zfs/zfsimpl.h b/sys/cddl/boot/zfs/zfsimpl.h
--- a/sys/cddl/boot/zfs/zfsimpl.h
+++ b/sys/cddl/boot/zfs/zfsimpl.h
@@ -76,7 +76,9 @@
 #define	AVL_PCMP(a, b)	\
 	(((uintptr_t)(a) > (uintptr_t)(b)) - ((uintptr_t)(a) < (uintptr_t)(b)))
 
+#if !defined(NEED_SOLARIS_BOOLEAN)	/* Only defined when we'll define this elsewhere */
 typedef enum { B_FALSE, B_TRUE } boolean_t;
+#endif
 
 /* CRC64 table */
 #define	ZFS_CRC64_POLY	0xC96C5795D7870F42ULL	/* ECMA-182, reflected form */