diff --git a/core/src/main/java/com/google/adk/models/GeminiUtil.java b/core/src/main/java/com/google/adk/models/GeminiUtil.java
index c3c38fa88..501b279b1 100644
--- a/core/src/main/java/com/google/adk/models/GeminiUtil.java
+++ b/core/src/main/java/com/google/adk/models/GeminiUtil.java
@@ -17,6 +17,7 @@
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
 
+import com.google.common.base.Ascii;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
@@ -128,7 +129,8 @@ public static LlmRequest sanitizeRequestForGeminiApi(LlmRequest llmRequest) {
    */
   static List<Content> ensureModelResponse(List<Content> contents) {
     // Last content must be from the user, otherwise the model won't respond.
-    if (contents.isEmpty() || !Iterables.getLast(contents).role().orElse("").equals("user")) {
+    if (contents.isEmpty()
+        || !Ascii.equalsIgnoreCase(Iterables.getLast(contents).role().orElse(""), "user")) {
       Content userContent =
           Content.builder()
               .parts(ImmutableList.of(Part.fromText(CONTINUE_OUTPUT_MESSAGE)))
diff --git a/core/src/test/java/com/google/adk/models/GeminiUtilTest.java b/core/src/test/java/com/google/adk/models/GeminiUtilTest.java
index 99df2cb50..0fae0767c 100644
--- a/core/src/test/java/com/google/adk/models/GeminiUtilTest.java
+++ b/core/src/test/java/com/google/adk/models/GeminiUtilTest.java
@@ -427,6 +427,17 @@ public void ensureModelResponse_userRoleIsLast_returnsSameList() {
     assertThat(result).containsExactly(modelContent, userContent).inOrder();
   }
 
+  @Test
+  public void ensureModelResponse_userRoleIsLastCaseInsensitive_returnsSameList() {
+    Content modelContent = Content.builder().role("model").build();
+    Content userContent = Content.builder().role("USER").build();
+    ImmutableList<Content> contents = ImmutableList.of(modelContent, userContent);
+
+    List<Content> result = GeminiUtil.ensureModelResponse(contents);
+
+    assertThat(result).containsExactly(modelContent, userContent).inOrder();
+  }
+
   @Test
   public void ensureModelResponse_lastContentIsNotUser_appendsContinueMessage() {
     Content modelContent1 = Content.builder().role("model").build();