diff --git a/tools/testing/kunit/qemu_configs/sh.py b/tools/testing/kunit/qemu_configs/sh.py
index 78a474a5b95f..f00cb89fdef6 100644
--- a/tools/testing/kunit/qemu_configs/sh.py
+++ b/tools/testing/kunit/qemu_configs/sh.py
@@ -7,7 +7,9 @@ CONFIG_CPU_SUBTYPE_SH7751R=y
 CONFIG_MEMORY_START=0x0c000000
 CONFIG_SH_RTS7751R2D=y
 CONFIG_RTS7751R2D_PLUS=y
-CONFIG_SERIAL_SH_SCI=y''',
+CONFIG_SERIAL_SH_SCI=y
+CONFIG_CMDLINE_EXTEND=y
+''',
 			   qemu_arch='sh4',
 			   kernel_path='arch/sh/boot/zImage',
 			   kernel_command_line='console=ttySC1',