diff --git a/core/src/main/java/com/google/adk/events/EventActions.java b/core/src/main/java/com/google/adk/events/EventActions.java
index 31b096930..4873a5f49 100644
--- a/core/src/main/java/com/google/adk/events/EventActions.java
+++ b/core/src/main/java/com/google/adk/events/EventActions.java
@@ -110,12 +110,12 @@ public void removeStateByKey(String key) {
   }
 
   @JsonProperty("artifactDelta")
-  public ConcurrentMap<String, Integer> artifactDelta() {
+  public Map<String, Integer> artifactDelta() {
     return artifactDelta;
   }
 
-  public void setArtifactDelta(ConcurrentMap<String, Integer> artifactDelta) {
-    this.artifactDelta = artifactDelta;
+  public void setArtifactDelta(Map<String, Integer> artifactDelta) {
+    this.artifactDelta = new ConcurrentHashMap<>(artifactDelta);
   }
 
   @JsonProperty("deletedArtifactIds")
@@ -322,8 +322,8 @@ public Builder stateDelta(ConcurrentMap<String, Object> value) {
 
     @CanIgnoreReturnValue
     @JsonProperty("artifactDelta")
-    public Builder artifactDelta(ConcurrentMap<String, Integer> value) {
-      this.artifactDelta = value;
+    public Builder artifactDelta(Map<String, Integer> value) {
+      this.artifactDelta = new ConcurrentHashMap<>(value);
       return this;
     }
 
diff --git a/core/src/test/java/com/google/adk/events/EventActionsTest.java b/core/src/test/java/com/google/adk/events/EventActionsTest.java
index 2975ca83f..22bb94e64 100644
--- a/core/src/test/java/com/google/adk/events/EventActionsTest.java
+++ b/core/src/test/java/com/google/adk/events/EventActionsTest.java
@@ -110,6 +110,16 @@ public void merge_mergesAllFields() {
     assertThat(merged.compaction()).hasValue(COMPACTION);
   }
 
+  @Test
+  public void setArtifactDelta_copiesRegularMap() {
+    EventActions eventActions = new EventActions();
+    ImmutableMap<String, Integer> artifactDelta = ImmutableMap.of("artifact1", 1);
+
+    eventActions.setArtifactDelta(artifactDelta);
+
+    assertThat(eventActions.artifactDelta()).containsExactly("artifact1", 1);
+  }
+
   @Test
   public void removeStateByKey_marksKeyAsRemoved() {
     EventActions eventActions = new EventActions();