diff --git a/indra/llrender/llrender.cpp b/indra/llrender/llrender.cpp
index cd827f5091eb4b1cc1c27379c6a36f35378cf6af..03a9884c2bcacde9122b842ea388ba549e8101c5 100644
--- a/indra/llrender/llrender.cpp
+++ b/indra/llrender/llrender.cpp
@@ -1434,6 +1434,8 @@ void LLRender::loadIdentity()
 	flush();
 
 	{
+		llassert_always(mMatrixMode < NUM_MATRIX_MODES) ;
+
 		mMatrix[mMatrixMode][mMatIdx[mMatrixMode]].make_identity();
 		mMatHash[mMatrixMode]++;
 	}