diff --git a/include/groundvm.h b/include/groundvm.h
index 601e496..7fbad50 100644
--- a/include/groundvm.h
+++ b/include/groundvm.h
@@ -58,6 +58,7 @@ typedef struct GroundError {
  */
 typedef struct GroundValue {
     GroundValueType type;
+    struct GroundStruct* customType;
     union {
         int64_t intVal;
         double doubleVal;