diff --git a/src/core/org/luaj/vm2/lib/BaseLib.java b/src/core/org/luaj/vm2/lib/BaseLib.java
index bdb12f44..0c2f43e0 100644
--- a/src/core/org/luaj/vm2/lib/BaseLib.java
+++ b/src/core/org/luaj/vm2/lib/BaseLib.java
@@ -478,7 +478,7 @@ public class BaseLib extends TwoArgFunction implements ResourceFinder {
 					return -1;
 			}
 			--remaining;
-			return bytes[offset++];
+			return 0xFF&bytes[offset++];
 		}
 	}
 }