diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
index 93789c5f06d2..8fdc6c2c72e4 100644
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -49,6 +49,7 @@ CLANG_NO_IAS34= -no-integrated-as
 .if ${COMPILER_VERSION} >= 40800
 # Catch-all for all the things that are in our tree, but for which we're
 # not yet ready for this compiler.
+NO_WUNUSED_BUT_SET_VARIABLE = -Wno-unused-but-set-variable
 CWARNEXTRA?=	-Wno-error=address				\
 		-Wno-error=aggressive-loop-optimizations	\
 		-Wno-error=array-bounds				\
diff --git a/sys/modules/bxe/Makefile b/sys/modules/bxe/Makefile
index 3470571d94ff..b9202e22c305 100644
--- a/sys/modules/bxe/Makefile
+++ b/sys/modules/bxe/Makefile
@@ -19,3 +19,4 @@ SRCS	+= bxe.c               \
 CFLAGS += -I${BXE}
 
 .include <bsd.kmod.mk>
+CWARNFLAGS+=	${NO_WUNUSED_BUT_SET_VARIABLE}
diff --git a/sys/modules/drm2/i915kms/Makefile b/sys/modules/drm2/i915kms/Makefile
index 91e771901245..45348b494ac0 100644
--- a/sys/modules/drm2/i915kms/Makefile
+++ b/sys/modules/drm2/i915kms/Makefile
@@ -68,3 +68,4 @@ CWARNFLAGS.i915_gem_tiling.c=	${NO_WTAUTOLOGICAL_POINTER_COMPARE}
 CWARNFLAGS.i915_gem_execbuffer.c=	${NO_WTAUTOLOGICAL_POINTER_COMPARE}
 CWARNFLAGS.intel_display.c=	${NO_WTAUTOLOGICAL_POINTER_COMPARE}
 CWARNFLAGS.intel_overlay.c=	${NO_WTAUTOLOGICAL_POINTER_COMPARE}
+CWARNFLAGS+=	${NO_WUNUSED_BUT_SET_VARIABLE}
diff --git a/sys/modules/drm2/radeonkms/Makefile b/sys/modules/drm2/radeonkms/Makefile
index ef50e70a60de..722a6a180680 100644
--- a/sys/modules/drm2/radeonkms/Makefile
+++ b/sys/modules/drm2/radeonkms/Makefile
@@ -118,3 +118,4 @@ CFLAGS+=			-I${SRCTOP}/sys/dev/drm2/radeon
 CWARNFLAGS.radeon_cp.c=		-Wno-unused-value
 CWARNFLAGS.r600_cp.c=		-Wno-unused-value
 CWARNFLAGS+=			${CWARNFLAGS.${.IMPSRC:T}}
+CWARNFLAGS+=	${NO_WUNUSED_BUT_SET_VARIABLE}