diff --git a/src/common/src/tdataformat.c b/src/common/src/tdataformat.c
index 9bcada27cbe0c54c18ebf6ab90e04de7ccb1a914..c4f3dda7b496c9eac9a0d615b9b9ca4d99d15647 100644
--- a/src/common/src/tdataformat.c
+++ b/src/common/src/tdataformat.c
@@ -25,7 +25,7 @@ static void tdMergeTwoDataCols(SDataCols *target, SDataCols *src1, int *iter1, i
 int tdAllocMemForCol(SDataCol *pCol, int maxPoints) {
   int spaceNeeded = pCol->bytes * maxPoints;
   if(IS_VAR_DATA_TYPE(pCol->type)) {
-    spaceNeeded += sizeof(VarDataOffsetT) * maxPoints;
+    spaceNeeded += sizeof(VarDataOffsetT) * maxPoints + sizeof(VarDataLenT) * maxPoints;
   }
   if(pCol->spaceSize < spaceNeeded) {
     void* ptr = realloc(pCol->pData, spaceNeeded);