diff --git a/pc-bios/spapr-rtas/Makefile b/pc-bios/spapr-rtas/Makefile
index f26dd428b7..4b9bb12306 100644
--- a/pc-bios/spapr-rtas/Makefile
+++ b/pc-bios/spapr-rtas/Makefile
@@ -14,8 +14,11 @@ $(call set-vpath, $(SRC_PATH)/pc-bios/spapr-rtas)
 
 build-all: spapr-rtas.bin
 
+%.o: %.S
+	$(call quiet-command,$(CCAS) -mbig -c -o $@ $<,"CCAS","$(TARGET_DIR)$@")
+
 %.img: %.o
-	$(call quiet-command,$(CC) -nostdlib -o $@ $<,"Building","$(TARGET_DIR)$@")
+	$(call quiet-command,$(CC) -nostdlib -mbig -o $@ $<,"Building","$(TARGET_DIR)$@")
 
 %.bin: %.img
 	$(call quiet-command,$(OBJCOPY) -O binary -j .text $< $@,"Building","$(TARGET_DIR)$@")