Index: boot/Makefile.build
===================================================================
--- boot/Makefile.build	(revision 4d32b16fd938c28a5c64a63ecae4066b192d867e)
+++ boot/Makefile.build	(revision 59d82352304d341674d06eca07ba9d7a4d7f7a41)
@@ -36,5 +36,4 @@
 DEFS = -DBOOT -DRELEASE=$(RELEASE) "-DCOPYRIGHT=$(COPYRIGHT)" "-DNAME=$(NAME)" -D__$(BITS)_BITS__ -D__$(ENDIANESS)__
 
-AFLAGS = --fatal-warnings
 LDFLAGS = -Wl,--fatal-warnings,--warn-common $(EXTRA_LDFLAGS)
 
@@ -42,5 +41,6 @@
 	-ffreestanding -nostdlib \
 	-fexec-charset=UTF-8 -finput-charset=UTF-8 -fno-common \
-	-fdebug-prefix-map=$(realpath $(ROOT_PATH))=.
+	-fdebug-prefix-map=$(realpath $(ROOT_PATH))=. \
+	-Wa,--fatal-warnings
 
 GCC_CFLAGS = -Wall -Wextra -Wno-unused-parameter -Wmissing-prototypes \
@@ -80,6 +80,4 @@
 -include $(DEPENDS)
 
-AS_CFLAGS := $(addprefix -Xassembler ,$(AFLAGS))
-
 $(BOOT_OUTPUT): $(RAW)
 	$(OBJCOPY) -O $(BFD_OUTPUT) $< $@
@@ -92,8 +90,8 @@
 
 %.o: %.s | depend
-	$(CC_JOB) -c -MD -MP $(DEFS) $(CFLAGS) $(AS_CFLAGS)
+	$(CC_JOB) -c -MD -MP $(DEFS) $(CFLAGS)
 
 %.o: %.S | depend
-	$(CC_JOB) -c -MD -MP $(DEFS) $(CFLAGS) $(AS_CFLAGS)
+	$(CC_JOB) -c -MD -MP $(DEFS) $(CFLAGS)
 
 %.o: %.c | depend