diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
index 91f089e6a115..78f263e496dc 100644
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -6,7 +6,8 @@
 CWARNFLAGS?=	-Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes \
 		-Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual \
 		-Wundef -Wno-pointer-sign -fformat-extensions \
-		-Wmissing-include-dirs -fdiagnostics-show-option
+		-Wmissing-include-dirs -fdiagnostics-show-option \
+		${CWARNEXTRA}
 #
 # The following flags are next up for working on:
 #	-Wextra
@@ -22,7 +23,7 @@ NO_WSHIFT_COUNT_OVERFLOW=	-Wno-shift-count-overflow
 # Several other warnings which might be useful in some cases, but not severe
 # enough to error out the whole kernel build.  Display them anyway, so there is
 # some incentive to fix them eventually.
-CWARNFLAGS+=	-Wno-error-tautological-compare
+CWARNEXTRA+=	-Wno-error-tautological-compare
 .endif
 
 #