--- a/Makefile.rules	2023-01-20 22:52:47.530898157 +0100
+++ b/Makefile.rules	2023-01-20 22:53:09.370565670 +0100
@@ -210,7 +210,7 @@
 # Set NODEP to "@true" in order to disable "depend".
 
 depend: $(DEP_FILES)
-	$(NODEP) $(OCAMLDEP) *.ml *.mli >$@ || { rm -f $@; exit 1; }
+	$(NODEP) $(OCAMLDEP) -ml-synonym .mll *.ml *.mli >$@ || { rm -f $@; exit 1; }
 
 .PHONY: clean
 clean:: genclean