diff --git a/_examples/expr/Makefile b/_examples/expr/Makefile
index 7fef9a866ba414bc607b46c835d5c3158a213963..d755fb1091b253e68fe11b131229d13fb2372d5b 100644
--- a/_examples/expr/Makefile
+++ b/_examples/expr/Makefile
@@ -1,9 +1,9 @@
 default:
-	go run ../../main.go yacc -l -p=expr -c=copyright.txt -o=y.wa expr.y
+	go run ../../main.go yacc -l -p=expr -c="copyright.txt" -o="y.wa" expr.y
 	go run ../../main.go y.wa
 
 dev:
-	go run ../../main.go yacc -l -p=expr -c=copyright.txt -o=y.wa.go expr.y
+	go run ../../main.go yacc -l -p=expr -c="copyright.txt" -o="y.wa.go" expr.y
 	go run y.wa.go
 
 clean: