diff --git a/panda/src/glstuff/glGraphicsBuffer_src.cxx b/panda/src/glstuff/glGraphicsBuffer_src.cxx
index 190f910e5c..cc3ddf54b5 100644
--- a/panda/src/glstuff/glGraphicsBuffer_src.cxx
+++ b/panda/src/glstuff/glGraphicsBuffer_src.cxx
@@ -514,5 +514,7 @@ close_buffer() {
   
   // Release the Gsg
   _gsg.clear();
+
+  _is_valid = false;
 }