diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
index 461c56f24cfb..11794b329140 100644
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -190,7 +190,7 @@ CFLAGS+=	${SSP_CFLAGS}
 # Allow user-specified additional warning flags, plus compiler and file
 # specific flag overrides, unless we've overriden this...
 .if ${MK_WARNS} != "no"
-CFLAGS+=	${CWARNFLAGS} ${CWARNFLAGS.${COMPILER_TYPE}}
+CFLAGS+=	${CWARNFLAGS:M*} ${CWARNFLAGS.${COMPILER_TYPE}}
 CFLAGS+=	${CWARNFLAGS.${.IMPSRC:T}}
 .endif
 
diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
index 3c6193d61726..05e62481952d 100644
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -214,7 +214,7 @@ CFLAGS+=	-fstack-protector
 CFLAGS+=	-gdwarf-2
 .endif
 
-CFLAGS+= ${CWARNFLAGS} ${CWARNFLAGS.${.IMPSRC:T}}
+CFLAGS+= ${CWARNFLAGS:M*} ${CWARNFLAGS.${.IMPSRC:T}}
 CFLAGS+= ${CFLAGS.${COMPILER_TYPE}} ${CFLAGS.${.IMPSRC:T}}
 
 # Tell bmake not to mistake standard targets for things to be searched for