diff --git a/PDF/src/hpdf_xref.c b/PDF/src/hpdf_xref.c
index 8651778209..205129487a 100644
--- a/PDF/src/hpdf_xref.c
+++ b/PDF/src/hpdf_xref.c
@@ -132,8 +132,8 @@ HPDF_Xref_Add  (HPDF_Xref  xref,
 
     header = (HPDF_Obj_Header *)obj;
 
-    if (header->obj_id & HPDF_OTYPE_DIRECT ||
-            header->obj_id & HPDF_OTYPE_INDIRECT)
+    if ((header->obj_id & HPDF_OTYPE_DIRECT) ||
+            (header->obj_id & HPDF_OTYPE_INDIRECT))
         return HPDF_SetError(xref->error, HPDF_INVALID_OBJECT, 0);
 
     if (xref->entries->count >= HPDF_LIMIT_MAX_XREF_ELEMENT) {