diff --git a/luaj-core/src/main/java/org/luaj/vm2/lib/DebugLib.java b/luaj-core/src/main/java/org/luaj/vm2/lib/DebugLib.java
index 74c7e3e6..ff921b36 100644
--- a/luaj-core/src/main/java/org/luaj/vm2/lib/DebugLib.java
+++ b/luaj-core/src/main/java/org/luaj/vm2/lib/DebugLib.java
@@ -440,10 +440,10 @@ public class DebugLib extends TwoArgFunction {
 	static final class upvaluejoin extends VarArgFunction {
 		@Override
 		public Varargs invoke(Varargs args) {
-			LuaClosure f1 = args.checkclosure(1);
 			int n1 = args.checkint(2);
-			LuaClosure f2 = args.checkclosure(3);
+			LuaClosure f1 = args.checkclosure(1);
 			int n2 = args.checkint(4);
+			LuaClosure f2 = args.checkclosure(3);
 			if (n1 < 1 || n1 > f1.upValues.length)
 				argerror("index out of range");
 			if (n2 < 1 || n2 > f2.upValues.length)