diff --git a/flow/pua/flatbuffers_builder.go b/flow/pua/flatbuffers_builder.go
index 024c1d0a1c..91afbccc84 100644
--- a/flow/pua/flatbuffers_builder.go
+++ b/flow/pua/flatbuffers_builder.go
@@ -160,7 +160,7 @@ func (b *Builder) WriteVtable(ls *lua.LState) int {
 	}
 
 	var existingVtable int
-	for i := len(b.ba.data) - 1; i >= 0; i-- {
+	for i := len(b.vtables) - 1; i >= 0; i -= 1 {
 		vt2Offset := b.vtables[i]
 		vt2Start := len(b.ba.data) - vt2Offset
 		vt2Len := uint16n.UnpackU64(b.ba.data[vt2Start:])
@@ -176,7 +176,7 @@ func (b *Builder) WriteVtable(ls *lua.LState) int {
 	}
 
 	if existingVtable == 0 {
-		for i := len(b.currentVT) - 1; i >= 0; i-- {
+		for i := len(b.currentVT) - 1; i >= 0; i -= 1 {
 			var off uint16
 			if b.currentVT[i] != 0 {
 				off = uint16(objectOffset - b.currentVT[i])