diff --git a/src/mesa/vbo/vbo_exec_draw.c b/src/mesa/vbo/vbo_exec_draw.c
index 5381cc4..0a8289a 100644
--- a/src/mesa/vbo/vbo_exec_draw.c
+++ b/src/mesa/vbo/vbo_exec_draw.c
@@ -374,10 +374,16 @@ void vbo_exec_vtx_flush( struct vbo_exec_context *exec,
 
    if (unmap) 
       exec->vtx.max_vert = 0;
-   else
-      exec->vtx.max_vert = ((VBO_VERT_BUFFER_SIZE - exec->vtx.buffer_used) / 
-                            (exec->vtx.vertex_size * sizeof(GLfloat)));
-
+   else {
+     if (exec->vtx.vertex_size != 0) {
+       exec->vtx.max_vert = ((VBO_VERT_BUFFER_SIZE - exec->vtx.buffer_used) / 
+			     (exec->vtx.vertex_size * sizeof(GLfloat)));
+       }
+     else {
+       exec->vtx.max_vert = ((VBO_VERT_BUFFER_SIZE - exec->vtx.buffer_used) / 
+			     sizeof(GLfloat));
+       }
+     }
 
    exec->vtx.buffer_ptr = exec->vtx.buffer_map;
    exec->vtx.prim_count = 0;