diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index 580df07cf866bed21faa17bead249fd4e9e9a65d..2a1974ede9569eec5fdcf45a3866eea1386b564b 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -2662,7 +2662,7 @@ bool getTopBotFuncEnv(SFunctionNode* pFunc, SFuncExecEnv* pEnv) {
 
 bool getTopBotMergeFuncEnv(SFunctionNode* pFunc, SFuncExecEnv* pEnv) {
   //intermediate result is binary and length contains VAR header size
-  pEnv->calcMemSize = pFunc->node.resType.bytes - VARSTR_HEADER_SIZE;
+  pEnv->calcMemSize = pFunc->node.resType.bytes;
   return true;
 }