diff --git a/src/duration.ts b/src/duration.ts
index 77de611..5abf035 100644
--- a/src/duration.ts
+++ b/src/duration.ts
@@ -182,6 +182,9 @@ export function roundToSingleUnit(duration: Duration, {relativeTo = Date.now()}:
     } else if (monthsDiff < 11) {
       months = monthsDiff
       years = 0
+    } else if (monthsDiff === 11) {
+      months = 0
+      years += 1 // the old behavior: "11 months" is rounded to "1 year"
     } else {
       months = 0
       years = yearDiff * sign