diff --git a/core/src/main/java/com/google/adk/tools/mcp/McpAsyncToolset.java b/core/src/main/java/com/google/adk/tools/mcp/McpAsyncToolset.java
index cb541eccf..d676ce9b8 100644
--- a/core/src/main/java/com/google/adk/tools/mcp/McpAsyncToolset.java
+++ b/core/src/main/java/com/google/adk/tools/mcp/McpAsyncToolset.java
@@ -127,7 +127,7 @@ public McpAsyncToolset build() {
    * @param objectMapper An ObjectMapper instance for parsing schemas.
    * @param toolFilter Either a ToolPredicate or a List of tool names.
    */
-  McpAsyncToolset(
+  protected McpAsyncToolset(
       McpSessionManager mcpSessionManager, ObjectMapper objectMapper, @Nullable Object toolFilter) {
     Objects.requireNonNull(mcpSessionManager);
     Objects.requireNonNull(objectMapper);