diff --git a/src/main/kotlin/org/kalasim/misc/TimeUtil.kt b/src/main/kotlin/org/kalasim/misc/TimeUtil.kt
index d7bd1477..2858cb5a 100644
--- a/src/main/kotlin/org/kalasim/misc/TimeUtil.kt
+++ b/src/main/kotlin/org/kalasim/misc/TimeUtil.kt
@@ -11,7 +11,11 @@ fun Iterable<Duration>.sum(): Duration = sumOf { it }
 
 /** Compute the sum of a set of durations via a selector function.*/
 fun <T> Iterable<T>.sumOf(selector: (T) -> Duration) = map { selector(it) }.run {
-    reduce { a, b -> a + b }
+    if(isEmpty()) {
+        Duration.ZERO
+    } else {
+        reduce { a, b -> a + b }
+    }
 }