diff --git a/MinimedKit/PumpManager/UnfinalizedDose.swift b/MinimedKit/PumpManager/UnfinalizedDose.swift
index 6298588..de9d0f7 100644
--- a/MinimedKit/PumpManager/UnfinalizedDose.swift
+++ b/MinimedKit/PumpManager/UnfinalizedDose.swift
@@ -117,7 +117,9 @@ public struct UnfinalizedDose: RawRepresentable, Equatable, CustomStringConverti
         
         let programmedUnits = units
         self.programmedUnits = programmedUnits
-        let newDuration = date.timeIntervalSince(startTime)
+
+        // Guard against negative duration if clock has changed
+        let newDuration = max(0, date.timeIntervalSince(startTime))
 
         switch doseType {
         case .bolus: