diff --git a/vivado/Makefile.rules b/vivado/Makefile.rules
index febdb80..2638a92 100644
--- a/vivado/Makefile.rules
+++ b/vivado/Makefile.rules
@@ -6,23 +6,27 @@ XSIM  ?= xsim
 
 vpath %.sv  $(PATH_SRC)
 vpath %.svh $(PATH_SRC)
-vpath %.sdb xsim.dir/work
+
+.SUFFIXES:
+.SUFFIXES: .sv .svh .sdb
 
 .PHONY: all clean sim_build sim sim_gui
 
 all: sim
 
-%.sdb: %.sv
+OBJS=$(subst sv,sdb,$(SOURCES))
+
+xsim.dir/work/%.sdb: %.sv $(INCLUDES)
 	$(XVLOG) --sv --nolog $<
 	rm xvlog.pb
 
-xsim.dir/work.$(TB)/xsim.dbg:	$(subst sv,sdb,$(SOURCES))
+xsim.dir/work.$(TB)/xsim.dbg:	$(addprefix xsim.dir/work/, $(OBJS))
 	$(XELAB) --nolog --debug all -Odisable_unused_removal $(TB)
 	rm -f xelab.pb
 
 sim_build:	xsim.dir/work.$(TB)/xsim.dbg
 
-sim:	sim_build
+sim:	xsim.dir/work.$(TB)/xsim.dbg
 	$(XSIM) --nolog --runall $(TB)
 	rm -f xsim.jou xsim_* webtalk*