diff --git a/biome-grid.el b/biome-grid.el
index 8977bd9..4c2df55 100644
--- a/biome-grid.el
+++ b/biome-grid.el
@@ -26,6 +26,7 @@
 
 ;;; Code:
 (require 'cl-lib)
+(require 'iso8601)
 (require 'ct)
 (require 'seq)
 (require 'tabulated-list)