diff --git a/sys/sys/_endian.h b/sys/sys/_endian.h
index ff909f532663..7ac39386e2e1 100644
--- a/sys/sys/_endian.h
+++ b/sys/sys/_endian.h
@@ -1,126 +1,130 @@
 /*-
  * SPDX-License-Identifier: BSD-3-Clause
  *
  * Copyright (c) 1987, 1991 Regents of the University of California.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. Neither the name of the University nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #ifndef _SYS__ENDIAN_H_
 #define	_SYS__ENDIAN_H_
 
 #if !defined(_MACHINE_ENDIAN_H_) && !defined(_BYTESWAP_H_) && !defined(_ENDIAN_H_)
 #error "sys/_endian.h should not be included directly"
 #endif
 
 /* BSD Compatiblity */
 #define	_BYTE_ORDER	__BYTE_ORDER__
 
 /*
  * Definitions for byte order, according to byte significance from low
- * address to high.
+ * address to high. We undefine any prior definition of them because
+ * powerpc compilers define _LITTLE_ENDIAN and _BIG_ENDIAN to mean
+ * something else.
  */
+#undef _LITTLE_ENDIAN
 #define	_LITTLE_ENDIAN	__ORDER_LITTLE_ENDIAN__ /* LSB first: 1234 */
+#undef _BIG_ENDIAN
 #define	_BIG_ENDIAN	__ORDER_BIG_ENDIAN__    /* MSB first: 4321 */
 #define	_PDP_ENDIAN	__ORDER_PDP_ENDIAN__    /* LSB first in word,
 						 * MSW first in long: 3412 */
 
 /*
  * Define the order of 32-bit words in 64-bit words.
  */
 #if _BYTE_ORDER == _LITTLE_ENDIAN
 #define	_QUAD_HIGHWORD	1
 #define	_QUAD_LOWWORD	0
 #elif _BYTE_ORDER == _BIG_ENDIAN
 #define	_QUAD_HIGHWORD	0
 #define	_QUAD_LOWWORD	1
 #else
 #error "Unsupported endian"
 #endif
 
 /*
  * Deprecated variants that don't have enough underscores to be useful in more
  * strict namespaces.
  */
 #if __BSD_VISIBLE
 #define	LITTLE_ENDIAN   _LITTLE_ENDIAN
 #define	BIG_ENDIAN      _BIG_ENDIAN
 #define	PDP_ENDIAN      _PDP_ENDIAN
 #define	BYTE_ORDER      _BYTE_ORDER
 #endif
 
 /* bswap primitives, based on compiler builtins */
 #define	__bswap16(x)	__builtin_bswap16(x)
 #define	__bswap32(x)	__builtin_bswap32(x)
 #define	__bswap64(x)	__builtin_bswap64(x)
 
 #if _BYTE_ORDER == _LITTLE_ENDIAN
 #define	__ntohl(x)	(__bswap32(x))
 #define	__ntohs(x)	(__bswap16(x))
 #define	__htonl(x)	(__bswap32(x))
 #define	__htons(x)	(__bswap16(x))
 #elif _BYTE_ORDER == _BIG_ENDIAN
 #define	__htonl(x)	((__uint32_t)(x))
 #define	__htons(x)	((__uint16_t)(x))
 #define	__ntohl(x)	((__uint32_t)(x))
 #define	__ntohs(x)	((__uint16_t)(x))
 #endif
 
 /*
  * Host to big endian, host to little endian, big endian to host, and little
  * endian to host byte order functions as detailed in byteorder(9).
  */
 #if _BYTE_ORDER == _LITTLE_ENDIAN
 #define	htobe16(x)	__bswap16((x))
 #define	htobe32(x)	__bswap32((x))
 #define	htobe64(x)	__bswap64((x))
 #define	htole16(x)	((uint16_t)(x))
 #define	htole32(x)	((uint32_t)(x))
 #define	htole64(x)	((uint64_t)(x))
 
 #define	be16toh(x)	__bswap16((x))
 #define	be32toh(x)	__bswap32((x))
 #define	be64toh(x)	__bswap64((x))
 #define	le16toh(x)	((uint16_t)(x))
 #define	le32toh(x)	((uint32_t)(x))
 #define	le64toh(x)	((uint64_t)(x))
 #else /* _BYTE_ORDER != _LITTLE_ENDIAN */
 #define	htobe16(x)	((uint16_t)(x))
 #define	htobe32(x)	((uint32_t)(x))
 #define	htobe64(x)	((uint64_t)(x))
 #define	htole16(x)	__bswap16((x))
 #define	htole32(x)	__bswap32((x))
 #define	htole64(x)	__bswap64((x))
 
 #define	be16toh(x)	((uint16_t)(x))
 #define	be32toh(x)	((uint32_t)(x))
 #define	be64toh(x)	((uint64_t)(x))
 #define	le16toh(x)	__bswap16((x))
 #define	le32toh(x)	__bswap32((x))
 #define	le64toh(x)	__bswap64((x))
 #endif /* _BYTE_ORDER == _LITTLE_ENDIAN */
 
 #endif /* _SYS__ENDIAN_H_ */