diff --git a/lib/Makefile.in b/lib/Makefile.in
index 995eac6..374ce33 100644
--- a/lib/Makefile.in
+++ b/lib/Makefile.in
@@ -88,7 +88,7 @@ ltds:
 	cp $(DTX.sty) $(DTX.cls) $(TDS.tex) $(TDSDIR.tex)
 	cp $(DTX.sty.ltxml) $(DTX.cls.ltxml) $(TDSDIR.tex) || echo "omitting ltxml files"
 	cp README $(DTX.pdf) $(EXAMPLE.tex) $(EXAMPLE.pdf) $(TDS.doc) $(TDSDIR.doc)
-	@ifneq ($(TDS.exdirs),"") then cp -R $(TDS.exdirs) $(TDSDIR.doc); fi
+	@ifneq ("$(TDS.exdirs)","") then cp -R $(TDS.exdirs) $(TDSDIR.doc); fi
 
 lctan:
 	mkdir -p $(CTANDIR)