diff --git a/src/gl/data/gl_vertexbuffer.cpp b/src/gl/data/gl_vertexbuffer.cpp
index 2faae2990..77623b3ca 100644
--- a/src/gl/data/gl_vertexbuffer.cpp
+++ b/src/gl/data/gl_vertexbuffer.cpp
@@ -398,6 +398,7 @@ void FFlatVertexBuffer::UpdatePlaneVertices(sector_t *sec, int plane)
 
 void FFlatVertexBuffer::CreateVBO()
 {
+	vbo_shadowdata.Reserve(mNumReserved);
 	CreateFlatVBO();
 	mCurIndex = mIndex = vbo_shadowdata.Size();
 	memcpy(map, &vbo_shadowdata[0], vbo_shadowdata.Size() * sizeof(FFlatVertex));