Index: share/mk/bsd.endian.mk
===================================================================
--- share/mk/bsd.endian.mk
+++ share/mk/bsd.endian.mk
@@ -16,5 +16,18 @@
 CAP_MKDB_ENDIAN= -b
 LOCALEDEF_ENDIAN= -b
 .else
+.if ${.MAKE.OS} == "FreeBSD"
 .error "Don't know the endian of this architecture"
+.else
+#
+# During bootstrapping on !FreeBSD OSes, we need to define some value.
+# Short of having an exhaustive list for all variants of Linux and MacOS
+# we return the unknown order and poison the other variables. They should
+# be unused during the bootstrap phases where we're building the bootstrap
+# tools.
+#
+TARGET_ENDIANNESS= unknown
+CAP_MKDB_ENDIAN= -B	# Poisoned value, invalid flags for both cap_mkdb
+LOCALEDEF_ENDIAN= -B	# and localedef.
+.endif
 .endif