diff --git a/hw/sun4m.c b/hw/sun4m.c
index e7a4cf6c92..a1373d4072 100644
--- a/hw/sun4m.c
+++ b/hw/sun4m.c
@@ -978,8 +978,11 @@ static void sun4m_hw_init(const struct sun4m_hwdef *hwdef, ram_addr_t RAM_size,
         fw_cfg_add_bytes(fw_cfg, FW_CFG_CMDLINE_DATA,
                          (uint8_t*)strdup(kernel_cmdline),
                          strlen(kernel_cmdline) + 1);
+        fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_SIZE,
+                       strlen(kernel_cmdline) + 1);
     } else {
         fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_CMDLINE, 0);
+        fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_SIZE, 0);
     }
     fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, INITRD_LOAD_ADDR);
     fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, 0); // not used