diff --git a/contrib/src/main/java/gov/nasa/jpl/aerie/contrib/streamline/modeling/polynomial/Polynomial.java b/contrib/src/main/java/gov/nasa/jpl/aerie/contrib/streamline/modeling/polynomial/Polynomial.java
index 7e00dd83a9..ea8db7c3ff 100644
--- a/contrib/src/main/java/gov/nasa/jpl/aerie/contrib/streamline/modeling/polynomial/Polynomial.java
+++ b/contrib/src/main/java/gov/nasa/jpl/aerie/contrib/streamline/modeling/polynomial/Polynomial.java
@@ -195,7 +195,7 @@ private Expiry findExpiryNearRoot(Predicate<Duration> expires) {
 
     // Do a binary search to find the exact transition time
     while (end.longerThan(start.plus(EPSILON))) {
-      Duration midpoint = start.plus(end).dividedBy(2);
+      Duration midpoint = start.plus(end.minus(start).dividedBy(2));
       if (expires.test(midpoint)) {
         end = midpoint;
       } else {