diff --git a/src/gallium/auxiliary/util/u_vbuf.c b/src/gallium/auxiliary/util/u_vbuf.c
index 7a6e214b29a..f88c92dd6ac 100644
--- a/src/gallium/auxiliary/util/u_vbuf.c
+++ b/src/gallium/auxiliary/util/u_vbuf.c
@@ -1152,7 +1152,7 @@ u_vbuf_get_minmax_index_mapped(const struct pipe_draw_info *info,
       break;
    }
    default:
-      assert(0);
+      unreachable("bad index size");
    }
 }