diff --git a/src/main.rs b/src/main.rs
index 439e715..5be1644 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -12,6 +12,9 @@ enum AppError {
 
     #[error("Toggl error: {0}")]
     TogglError(#[from] toggl::TogglError),
+
+    #[error("User modified since time delta is too large. Max allowed is 90 days.")]
+    LookBackTooLarge,
 }
 
 struct Worker {
@@ -53,6 +56,10 @@ impl Worker {
     }
 
     async fn fetch_changed_since(&mut self, look_back: TimeDelta) -> Result<(), AppError> {
+        if look_back > TimeDelta::days(90) {
+            return Err(AppError::LookBackTooLarge)
+        }
+
         self.update_time_entries(Utc::now() - look_back).await
     }