diff --git a/mug/src/main/java/com/google/mu/util/stream/BiStream.java b/mug/src/main/java/com/google/mu/util/stream/BiStream.java
index b91b3e5335..68dd504d12 100644
--- a/mug/src/main/java/com/google/mu/util/stream/BiStream.java
+++ b/mug/src/main/java/com/google/mu/util/stream/BiStream.java
@@ -363,7 +363,7 @@ public static <K, V> Builder<K, V> builder() {
     requireNonNull(right);
     return collectingAndThen(
         toList(),
-        left ->
+        (List<L> left) ->
             // If `right` is infinite, even limit(1) will result in infinite loop otherwise.
             left.isEmpty() ? empty() : concat(right.map(r -> from(left, identity(), l -> r))));
   }