diff --git a/drivers/platform/chrome/cros_ec_lightbar.c b/drivers/platform/chrome/cros_ec_lightbar.c
index d7e9928e263d..f70076c9d037 100644
--- a/drivers/platform/chrome/cros_ec_lightbar.c
+++ b/drivers/platform/chrome/cros_ec_lightbar.c
@@ -505,9 +505,14 @@ static ssize_t program_store(struct device *dev, struct device_attribute *attr,
 			return -EINVAL;
 		}
 	} else {
+		/*
+		 * Bound the payload strictly by the maximum value the structural
+		 * size field can natively support.
+		 */
 		extra_bytes = offsetof(typeof(*param), set_program_ex) +
 			sizeof(param->set_program_ex);
-		max_size = ec->ec_dev->max_request - extra_bytes;
+		max_size = min_t(size_t, ec->ec_dev->max_request - extra_bytes,
+				 type_max(typeof(param->set_program_ex.size)));
 	}
 
 	msg = alloc_lightbar_cmd_msg(ec);