diff --git a/runtime/luajit.lua b/runtime/luajit.lua
index 2de1069..90a9afc 100644
--- a/runtime/luajit.lua
+++ b/runtime/luajit.lua
@@ -240,6 +240,7 @@ do
 	trunc.u64_f64 = truncate_i64
 
 	function extend.u64_i32(num)
+		RE_INSTANCE.i64 = 0
 		RE_INSTANCE.i32 = num
 
 		return RE_INSTANCE.i64