Index: kernel/Makefile.build
===================================================================
--- kernel/Makefile.build	(revision 36e9cd186877d97860a6d53672806bfac213cfa4)
+++ kernel/Makefile.build	(revision b32c604f4c266680482da12fcd5d10bfc96fa4a6)
@@ -55,10 +55,10 @@
 	-fexec-charset=UTF-8 -fwide-exec-charset=UTF-32$(ENDIANESS) \
 	-finput-charset=UTF-8 -ffreestanding -fno-builtin -nostdlib -nostdinc \
-	-Wall -Wextra -Wno-unused-parameter -Wmissing-prototypes -Werror \
-	-pipe
+	-Wall -Wextra -Wno-unused-parameter -Wmissing-prototypes \
+	-Werror-implicit-function-declaration -Werror -pipe
 
 ICC_CFLAGS = -I$(INCLUDES) -O$(OPTIMIZATION) -imacros ../config.h \
 	-ffreestanding -fno-builtin -nostdlib -nostdinc -Wall -Wmissing-prototypes \
-	-Werror -wd170
+	-Werror-implicit-function-declaration -Werror -wd170
 
 SUNCC_CFLAGS = -I$(INCLUDES) -xO$(OPTIMIZATION) \