diff --git a/util/cbfstool/Makefile.inc b/util/cbfstool/Makefile.inc
index 5b49fe80ad..47b89e57b0 100644
--- a/util/cbfstool/Makefile.inc
+++ b/util/cbfstool/Makefile.inc
@@ -95,7 +95,6 @@ TOOLCFLAGS += -Wstrict-prototypes -Wwrite-strings
 TOOLCFLAGS += -O2
 TOOLCPPFLAGS ?= -D_DEFAULT_SOURCE # memccpy() from string.h
 TOOLCPPFLAGS += -D_BSD_SOURCE -D_SVID_SOURCE # _DEFAULT_SOURCE for older glibc
-TOOLCPPFLAGS += -D_XOPEN_SOURCE=700 # strdup() from string.h
 TOOLCPPFLAGS += -D_GNU_SOURCE # memmem() from string.h
 TOOLCPPFLAGS += -I$(top)/util/cbfstool/flashmap
 TOOLCPPFLAGS += -I$(top)/util/cbfstool
@@ -113,6 +112,10 @@ TOOLCPPFLAGS += -I$(top)/src/vendorcode/intel/edk2/uefi_2.4/MdePkg/Include
 TOOLLDFLAGS ?=
 HOSTCFLAGS += -fms-extensions
 
+ifneq ($(shell uname -o 2>/dev/null), FreeBSD)
+TOOLCPPFLAGS += -D_XOPEN_SOURCE=700 # strdup() from string.h
+endif
+
 ifeq ($(shell uname -s | cut -c-7 2>/dev/null), MINGW32)
 TOOLCFLAGS += -mno-ms-bitfields
 endif