diff --git a/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java b/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java
index 45fbf80b..fa26530c 100644
--- a/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java
+++ b/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java
@@ -23,7 +23,6 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.introspect.AnnotatedMember;
 import com.fasterxml.jackson.databind.introspect.BeanPropertyDefinition;
-import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
 import com.google.adk.JsonBaseModel;
 import com.google.common.base.Strings;
 import com.google.genai.types.FunctionDeclaration;
@@ -45,9 +44,8 @@
 /** Utility class for function calling. */
 public final class FunctionCallingUtils {
 
-  private static final ObjectMapper OBJECT_MAPPER =
-      new ObjectMapper().registerModule(new Jdk8Module());
   private static final Logger logger = LoggerFactory.getLogger(FunctionCallingUtils.class);
+  private static final ObjectMapper OBJECT_MAPPER = JsonBaseModel.getMapper();
 
   /** Holds the state during a single schema generation process to handle caching and recursion. */
   private static class SchemaGenerationContext {
diff --git a/core/src/main/java/com/google/adk/tools/FunctionTool.java b/core/src/main/java/com/google/adk/tools/FunctionTool.java
index 3037ef40..73d22f8d 100644
--- a/core/src/main/java/com/google/adk/tools/FunctionTool.java
+++ b/core/src/main/java/com/google/adk/tools/FunctionTool.java
@@ -18,7 +18,7 @@
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
+import com.google.adk.JsonBaseModel;
 import com.google.adk.agents.InvocationContext;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -42,9 +42,9 @@
 
 /** FunctionTool implements a customized function calling tool. */
 public class FunctionTool extends BaseTool {
-  private static final ObjectMapper OBJECT_MAPPER =
-      new ObjectMapper().registerModule(new Jdk8Module());
+
   private static final Logger logger = LoggerFactory.getLogger(FunctionTool.class);
+  private static final ObjectMapper OBJECT_MAPPER = JsonBaseModel.getMapper();
 
   @Nullable private final Object instance;
   private final Method func;