diff --git a/sys/winnt/Makefile.gcc b/sys/winnt/Makefile.gcc
index e9d7bbf6e..d19532369 100644
--- a/sys/winnt/Makefile.gcc
+++ b/sys/winnt/Makefile.gcc
@@ -1753,7 +1753,7 @@ $(O)vision.o: vision.c $(HACK_H) $(INCL)/vis_tab.h
 $(O)weapon.o: weapon.c $(HACK_H)
 $(O)were.o: were.c $(HACK_H)
 $(O)wield.o: wield.c $(HACK_H)
-$(O)windmain.o: $(MSWSYS)\windmain.c $(HACK_H)
+$(O)windmain.o: $(MSWSYS)/windmain.c $(HACK_H)
 $(O)windows.o: windows.c $(HACK_H) $(INCL)/wingem.h $(INCL)/winGnome.h
 $(O)wizard.o: wizard.c $(HACK_H) $(INCL)/qtext.h
 $(O)worm.o: worm.c $(HACK_H) $(INCL)/lev.h