diff --git a/sys/boot/efi/libefi/Makefile b/sys/boot/efi/libefi/Makefile
index df37f31b8d0..60cb43f0274 100644
--- a/sys/boot/efi/libefi/Makefile
+++ b/sys/boot/efi/libefi/Makefile
@@ -16,4 +16,8 @@ CFLAGS+= -I${.CURDIR}/../../../../lib/libstand
 # Pick up the bootstrap header for some interface items
 CFLAGS+= -I${.CURDIR}/../../common
 
+ 
+# Suppress warning from clang for FreeBSD %b and %D formats
+CFLAGS+= -fformat-extensions
+
 .include <bsd.lib.mk>
diff --git a/sys/boot/i386/libi386/Makefile b/sys/boot/i386/libi386/Makefile
index e40f8b6bb1b..6b7e056d7d1 100644
--- a/sys/boot/i386/libi386/Makefile
+++ b/sys/boot/i386/libi386/Makefile
@@ -55,6 +55,9 @@ CFLAGS+=	-I${.CURDIR}/../../common -I${.CURDIR}/../common \
 # the location of libstand
 CFLAGS+=	-I${.CURDIR}/../../../../lib/libstand/
 
+# Suppress warning from clang for FreeBSD %b and %D formats
+CFLAGS+= -fformat-extensions
+
 .if ${MACHINE_CPUARCH} == "amd64"
 CLEANFILES+=	machine
 machine: