diff --git a/Makefile b/Makefile
index 28f9943..1f77dea 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,7 @@ clean:
 	rm -rf jars/
 
 jars/result.jar: jars/classes.jar
-	proguard -include proguard.conf -libraryjars $(HEADERS) -keepclassmembers class $(CLASSNAME) { public \<methods\> ';' } -keep public class $(CLASSNAME)
+	$(PROGUARD) -include proguard.conf -libraryjars $(HEADERS) -libraryjars $(JAVA_HOME)/jre/lib/rt.jar -keepclassmembers class $(CLASSNAME) { public \<methods\> ';' } -keep public class $(CLASSNAME)
 
 release jars/release.jar: jars/result.jar
 	-$(RETROTRANSLATOR) -srcjar jars/result.jar -destjar jars/release.jar