1 files changed, 8 insertions, 2 deletions
diff --git a/src/mesa/vbo/vbo_context.h b/src/mesa/vbo/vbo_context.h
index 1e85335c107..e6b9d890d5f 100644
--- a/src/mesa/vbo/vbo_context.h
+++ b/src/mesa/vbo/vbo_context.h
@@ -205,8 +205,14 @@ vbo_get_default_vals_as_union(GLenum format)
 static inline unsigned
 vbo_compute_max_verts(const struct vbo_exec_context *exec)
 {
-   return (VBO_VERT_BUFFER_SIZE - exec->vtx.buffer_used) /
-          (exec->vtx.vertex_size * sizeof(GLfloat));
+   unsigned n = (VBO_VERT_BUFFER_SIZE - exec->vtx.buffer_used) /
+      (exec->vtx.vertex_size * sizeof(GLfloat));
+   assert(n > 0);
+   /* Subtract one so we're always sure to have room for an extra
+    * vertex for GL_LINE_LOOP -> GL_LINE_STRIP conversion.
+    */
+   n--;
+   return n;
 }