diff --git a/sys/alpha/include/endian.h b/sys/alpha/include/endian.h
index 968d78c0542a..7906ea1eb7d8 100644
--- a/sys/alpha/include/endian.h
+++ b/sys/alpha/include/endian.h
@@ -112,11 +112,20 @@ __bswap16(__uint16_t __x)
 	return (__r);
 }
 
-#endif /* __GNUC__ */
-
 #define	__htonl(x)	__bswap32(x)
 #define	__htons(x)	__bswap16(x)
 #define	__ntohl(x)	__bswap32(x)
 #define	__ntohs(x)	__bswap16(x)
 
+#else /* !__GNUC__ */
+
+/*
+ * No optimizations are available for this compiler.  Fall back to
+ * non-optimized functions by defining the constant usually used to prevent
+ * redefinition.
+ */
+#define	_BYTEORDER_FUNC_DEFINED
+
+#endif /* __GNUC__ */
+
 #endif /* !_MACHINE_ENDIAN_H_ */
diff --git a/sys/amd64/include/endian.h b/sys/amd64/include/endian.h
index c979683c64e7..723a5f3d4fea 100644
--- a/sys/amd64/include/endian.h
+++ b/sys/amd64/include/endian.h
@@ -109,11 +109,20 @@ __bswap16(__uint16_t _x)
 	return (__byte_swap_word(_x));
 }
 
-#endif /* __GNUC__ */
-
 #define	__htonl(x)	__bswap32(x)
 #define	__htons(x)	__bswap16(x)
 #define	__ntohl(x)	__bswap32(x)
 #define	__ntohs(x)	__bswap16(x)
 
+#else /* !__GNUC__ */
+
+/*
+ * No optimizations are available for this compiler.  Fall back to
+ * non-optimized functions by defining the constant usually used to prevent
+ * redefinition.
+ */
+#define	_BYTEORDER_FUNC_DEFINED
+
+#endif /* __GNUC__ */
+
 #endif /* !_MACHINE_ENDIAN_H_ */
diff --git a/sys/i386/include/endian.h b/sys/i386/include/endian.h
index c8b86eed3516..d68653259ecb 100644
--- a/sys/i386/include/endian.h
+++ b/sys/i386/include/endian.h
@@ -117,11 +117,20 @@ __bswap16(__uint16_t _x)
 	return (__byte_swap_word(_x));
 }
 
-#endif /* __GNUC__ */
-
 #define	__htonl(x)	__bswap32(x)
 #define	__htons(x)	__bswap16(x)
 #define	__ntohl(x)	__bswap32(x)
 #define	__ntohs(x)	__bswap16(x)
 
+#else /* !__GNUC__ */
+
+/*
+ * No optimizations are available for this compiler.  Fall back to
+ * non-optimized functions by defining the constant usually used to prevent
+ * redefinition.
+ */
+#define	_BYTEORDER_FUNC_DEFINED
+
+#endif /* __GNUC__ */
+
 #endif /* !_MACHINE_ENDIAN_H_ */
diff --git a/sys/ia64/include/endian.h b/sys/ia64/include/endian.h
index 7ba8bbfbb999..c3d42cc2fbd9 100644
--- a/sys/ia64/include/endian.h
+++ b/sys/ia64/include/endian.h
@@ -93,11 +93,20 @@ __bswap16(__uint16_t __x)
 	return (__bswap64(__x) >> 48);
 }
 
-#endif /* __GNUC__ */
-
 #define	__htonl(x)	__bswap32(x)
 #define	__htons(x)	__bswap16(x)
 #define	__ntohl(x)	__bswap32(x)
 #define	__ntohs(x)	__bswap16(x)
 
+#else /* !__GNUC__ */
+
+/*
+ * No optimizations are available for this compiler.  Fall back to
+ * non-optimized functions by defining the constant usually used to prevent
+ * redefinition.
+ */
+#define	_BYTEORDER_FUNC_DEFINED
+
+#endif /* __GNUC__ */
+
 #endif /* !_MACHINE_ENDIAN_H_ */
diff --git a/sys/powerpc/include/endian.h b/sys/powerpc/include/endian.h
index a0f08a057991..5d1c1cacad90 100644
--- a/sys/powerpc/include/endian.h
+++ b/sys/powerpc/include/endian.h
@@ -95,11 +95,20 @@ __bswap64(__uint64_t _x)
 	    ((_x << 40) & ((__uint64_t)0xff << 48)) | ((_x << 56)));
 }
 
-#endif /* __GNUC__ */
-
 #define	__htonl(x)	((__uint32_t)(x))
 #define	__htons(x)	((__uint16_t)(x))
 #define	__ntohl(x)	((__uint32_t)(x))
 #define	__ntohs(x)	((__uint16_t)(x))
 
+#else /* !__GNUC__ */
+
+/*
+ * No optimizations are available for this compiler.  Fall back to
+ * non-optimized functions by defining the constant usually used to prevent
+ * redefinition.
+ */
+#define	_BYTEORDER_FUNC_DEFINED
+
+#endif /* __GNUC__ */
+
 #endif /* !_MACHINE_ENDIAN_H_ */
diff --git a/sys/sparc64/include/endian.h b/sys/sparc64/include/endian.h
index e8ee18400ae2..f10032c62799 100644
--- a/sys/sparc64/include/endian.h
+++ b/sys/sparc64/include/endian.h
@@ -94,11 +94,20 @@ __bswap64(__uint64_t _x)
 	    ((_x << 40) & ((__uint64_t)0xff << 48)) | ((_x << 56)));
 }
 
-#endif /* __GNUC__ */
-
 #define	__htonl(x)	((__uint32_t)(x))
 #define	__htons(x)	((__uint16_t)(x))
 #define	__ntohl(x)	((__uint32_t)(x))
 #define	__ntohs(x)	((__uint16_t)(x))
 
+#else /* !__GNUC__ */
+
+/*
+ * No optimizations are available for this compiler.  Fall back to
+ * non-optimized functions by defining the constant usually used to prevent
+ * redefinition.
+ */
+#define	_BYTEORDER_FUNC_DEFINED
+
+#endif /* __GNUC__ */
+
 #endif /* !_MACHINE_ENDIAN_H_ */