diff --git a/common/src/main/java/dev/cel/common/CelContainer.java b/common/src/main/java/dev/cel/common/CelContainer.java
index ee33c1da0..6d9fcd612 100644
--- a/common/src/main/java/dev/cel/common/CelContainer.java
+++ b/common/src/main/java/dev/cel/common/CelContainer.java
@@ -252,7 +252,13 @@ public ImmutableSet<String> resolveCandidateNames(String typeName) {
     return candidates.add(typeName).build();
   }
 
-  public abstract Builder toBuilder();
+  abstract Builder autoToBuilder();
+
+  public Builder toBuilder() {
+    Builder builder = autoToBuilder();
+    builder.aliases.putAll(aliases());
+    return builder;
+  }
 
   public static Builder newBuilder() {
     return new AutoValue_CelContainer.Builder().setName("");
diff --git a/common/src/test/java/dev/cel/common/CelContainerTest.java b/common/src/test/java/dev/cel/common/CelContainerTest.java
index ab1b322b9..f116039c8 100644
--- a/common/src/test/java/dev/cel/common/CelContainerTest.java
+++ b/common/src/test/java/dev/cel/common/CelContainerTest.java
@@ -198,4 +198,15 @@ public void containerBuilder_addAbbreviationsCollidesWithContainer_throws() {
             "abbreviation collides with container name: name=my.alias.a, abbreviation=a,"
                 + " container=a.b.c.M.N");
   }
+
+  @Test
+  public void container_toBuilderRoundTrip_retainsExistingProperties() {
+    CelContainer container =
+        CelContainer.newBuilder().setName("hello").addAlias("foo", "x.y").build();
+
+    container = container.toBuilder().addAlias("bar", "a.b").build();
+
+    assertThat(container.name()).isEqualTo("hello");
+    assertThat(container.aliases()).containsExactly("foo", "x.y", "bar", "a.b").inOrder();
+  }
 }