diff --git a/transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java b/transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java
index ad4e29cc1..4b93cfe22 100644
--- a/transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java
+++ b/transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java
@@ -415,7 +415,12 @@ public HTTPRestResponse subscribeToTask(ServerCallContext context, String tenant
      */
     public HTTPRestResponse getTask(ServerCallContext context, String tenant, String taskId, @Nullable Integer historyLength) {
         try {
-            TaskQueryParams params = new TaskQueryParams(taskId, historyLength, tenant);
+            TaskQueryParams params;
+            try {
+                params = new TaskQueryParams(taskId, historyLength, tenant);
+            } catch (IllegalArgumentException e) {
+                throw new InvalidParamsError(e.getMessage());
+            }
             Task task = requestHandler.onGetTask(params, context);
             if (task != null) {
                 return createSuccessResponse(200, io.a2a.grpc.Task.newBuilder(ProtoUtils.ToProto.task(task)));
diff --git a/transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java b/transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java
index f896f0af2..a8fefe07c 100644
--- a/transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java
+++ b/transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java
@@ -58,6 +58,17 @@ public void testGetTaskNotFound() {
         Assertions.assertTrue(response.getBody().contains("TaskNotFoundError"));
     }
 
+    @Test
+    public void testGetTaskNegativeHistoryLengthReturns422() {
+        RestHandler handler = new RestHandler(CARD, requestHandler, internalExecutor);
+
+        RestHandler.HTTPRestResponse response = handler.getTask(callContext, "", MINIMAL_TASK.id(), -1);
+
+        Assertions.assertEquals(422, response.getStatusCode());
+        Assertions.assertEquals("application/problem+json", response.getContentType());
+        Assertions.assertTrue(response.getBody().contains("InvalidParamsError"));
+    }
+
     @Test
     public void testListTasksStatusWireString() {
         RestHandler handler = new RestHandler(CARD, requestHandler, internalExecutor);