diff --git a/tools/libs/util/Makefile b/tools/libs/util/Makefile
index e016baf888..c3b21875dc 100644
--- a/tools/libs/util/Makefile
+++ b/tools/libs/util/Makefile
@@ -40,6 +40,14 @@ include $(XEN_ROOT)/tools/libs/libs.mk
 
 $(OBJS-y) $(PIC_OBJS): $(AUTOINCS)
 
+# Adding the .c conterparts of the headers generated by flex/bison as
+# prerequisite of all objects.
+# This is to tell make that if only the .c file is out-of-date but not the
+# header, it should still wait for the .c file to be rebuilt.
+# Otherwise, make doesn't considered "%.c %.h" as grouped targets, and will run
+# the flex/bison rules in parallel of CC rules which only need the header.
+$(OBJS-y) $(PIC_OBJS): libxlu_cfg_l.c libxlu_cfg_y.c libxlu_disk_l.c
+
 %.c %.h:: %.y
 	@rm -f $*.[ch]
 	$(BISON) --output=$*.c $<