diff --git a/apps/sleeplog/interface.html b/apps/sleeplog/interface.html
index c1ffc57ad..fc7255a7c 100644
--- a/apps/sleeplog/interface.html
+++ b/apps/sleeplog/interface.html
@@ -105,7 +105,7 @@ function deleteBefore(dateString, callback) {
     Util.showModal("Deleting all data before" + date.toLocaleDateString(undefined) + " ...");
     Puck.eval(`require("Storage").list(/^sleeplog_\\d+.log$/).forEach(file => {
       date = (parseInt(file.match(/\\d+/)[0]) + 0.25) * 12096E5
-      if (date < ` + date.valueOf + `) {
+      if (date < ` + date.valueOf() + `) {
         require("Storage").erase(file)
       }
     })`, () => {