diff --git a/export/planloader/planloader.h b/export/planloader/planloader.h
index c8a28533..410328c3 100644
--- a/export/planloader/planloader.h
+++ b/export/planloader/planloader.h
@@ -8,7 +8,7 @@ using SerializedPlan = struct {
   // If set, contains a serialized ::substrait::proto::Plan object.
   char *buffer;
   // If buffer is set, this is the size of the buffer.
-  uint32_t size;
+  int32_t size;
   // If null the buffer is valid, otherwise this points to an error message.
   char *errorMessage;
 };