diff --git a/Makefile b/Makefile
index e56889e228..ff33b4cec0 100644
--- a/Makefile
+++ b/Makefile
@@ -432,7 +432,7 @@ $(obj)include/autoconf.mk: $(obj)include/config.h $(VERSION_FILE)
 	@$(XECHO) Generating include/autoconf.mk ; \
 	set -e ; \
 	: Generate the dependancies ; \
-	$(CC) -M $(HOST_CFLAGS) $(CPPFLAGS) -MQ $@ include/common.h > $@.dep ; \
+	$(CC) -x c -M $(HOST_CFLAGS) $(CPPFLAGS) -MQ $@ include/common.h > $@.dep ; \
 	: Extract the config macros ; \
 	$(CPP) $(CFLAGS) -dM include/common.h | sed -n -f tools/scripts/define2mk.sed > $@