diff --git a/java/com/google/gerrit/truth/ListSubject.java b/java/com/google/gerrit/truth/ListSubject.java
index bee7408..9f93964 100644
--- a/java/com/google/gerrit/truth/ListSubject.java
+++ b/java/com/google/gerrit/truth/ListSubject.java
@@ -30,10 +30,10 @@
 public class ListSubject<S extends Subject, E> extends IterableSubject {
 
   private final List<E> list;
-  private final BiFunction<StandardSubjectBuilder, E, S> elementSubjectCreator;
+  private final BiFunction<StandardSubjectBuilder, ? super E, ? extends S> elementSubjectCreator;
 
   public static <S extends Subject, E> ListSubject<S, E> assertThat(
-      List<E> list, Subject.Factory<S, E> subjectFactory) {
+      List<E> list, Subject.Factory<? extends S, ? super E> subjectFactory) {
     return assertAbout(elements()).thatCustom(list, subjectFactory);
   }
 
@@ -44,7 +44,7 @@
   private ListSubject(
       FailureMetadata failureMetadata,
       List<E> list,
-      BiFunction<StandardSubjectBuilder, E, S> elementSubjectCreator) {
+      BiFunction<StandardSubjectBuilder, ? super E, ? extends S> elementSubjectCreator) {
     super(failureMetadata, list);
     this.list = list;
     this.elementSubjectCreator = elementSubjectCreator;
@@ -78,12 +78,13 @@
     }
 
     public <S extends Subject, E> ListSubject<S, E> thatCustom(
-        List<E> list, Subject.Factory<S, E> subjectFactory) {
+        List<E> list, Subject.Factory<? extends S, ? super E> subjectFactory) {
       return that(list, (builder, element) -> builder.about(subjectFactory).that(element));
     }
 
     public <S extends Subject, E> ListSubject<S, E> that(
-        List<E> list, BiFunction<StandardSubjectBuilder, E, S> elementSubjectCreator) {
+        List<E> list,
+        BiFunction<StandardSubjectBuilder, ? super E, ? extends S> elementSubjectCreator) {
       return new ListSubject<>(metadata(), list, elementSubjectCreator);
     }
   }
diff --git a/java/com/google/gerrit/truth/OptionalSubject.java b/java/com/google/gerrit/truth/OptionalSubject.java
index a87dff1..1c288be 100644
--- a/java/com/google/gerrit/truth/OptionalSubject.java
+++ b/java/com/google/gerrit/truth/OptionalSubject.java
@@ -39,7 +39,7 @@
   }
 
   public static <S extends Subject, T> OptionalSubject<S, T> assertThat(
-      Optional<T> optional, Subject.Factory<S, T> valueSubjectFactory) {
+      Optional<T> optional, Subject.Factory<? extends S, ? super T> valueSubjectFactory) {
     return assertAbout(optionals()).thatCustom(optional, valueSubjectFactory);
   }
 
@@ -91,7 +91,7 @@
     }
 
     public <S extends Subject, T> OptionalSubject<S, T> thatCustom(
-        Optional<T> optional, Subject.Factory<S, T> valueSubjectFactory) {
+        Optional<T> optional, Subject.Factory<? extends S, ? super T> valueSubjectFactory) {
       return that(optional, (builder, value) -> builder.about(valueSubjectFactory).that(value));
     }