diff --git a/config.mk b/config.mk
index 81c2584..f71e145 100644
--- a/config.mk
+++ b/config.mk
@@ -213,6 +213,10 @@ endif
 # TODO(sjg@chromium.org): Is this correct on Mac OS?
 ifdef CONFIG_FIT_SIGNATURE
 HOSTLIBS	+= -lssl -lcrypto
+
+# This affects include/image.h, but including the board config file
+# is tricky, so manually define this options here.
+HOSTCFLAGS	+= -DCONFIG_FIT_SIGNATURE
 endif
 
 ifneq ($(CONFIG_SYS_TEXT_BASE),)