diff --git a/indra/llrender/llrender.cpp b/indra/llrender/llrender.cpp
index 5eec0c553..133614e0d 100644
--- a/indra/llrender/llrender.cpp
+++ b/indra/llrender/llrender.cpp
@@ -1446,6 +1446,8 @@ void LLRender::loadIdentity()
 	flush();
 
 	{
+		llassert_always(mMatrixMode < NUM_MATRIX_MODES) ;
+
 		mMatrix[mMatrixMode][mMatIdx[mMatrixMode]].make_identity();
 		mMatHash[mMatrixMode]++;
 	}