diff --git a/lunatask/habits.go b/lunatask/habits.go
index 72805c14fc9e0a4df405f9000420fda3c9abcfe5..8593a2cec2c4365545e011059bb4aa61400e8778 100644
--- a/lunatask/habits.go
+++ b/lunatask/habits.go
@@ -19,7 +19,7 @@ import (
 
 // TrackHabitActivityRequest represents the request to track a habit activity
 type TrackHabitActivityRequest struct {
-	PerformedOn string `json:"performed_on" validate:"required,datetime"`
+	PerformedOn string `json:"performed_on" validate:"required,datetime=2006-01-02T15:04:05Z07:00"`
 }
 
 // TrackHabitActivityResponse represents the response from Lunatask API when tracking a habit activity