diff --git a/arch/Kconfig b/arch/Kconfig
index e61a7528ba..6c4b81a486 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -121,6 +121,7 @@ config SANDBOX
 	select SUPPORT_OF_CONTROL
 	select SYSRESET_CMD_POWEROFF
 	select IRQ
+	select SUPPORT_EXTENSION_SCAN
 	imply BITREVERSE
 	select BLOBLIST
 	imply CMD_DM
@@ -165,6 +166,7 @@ config SANDBOX
 	imply BOOTARGS_SUBST
 	imply PHY_FIXED
 	imply DM_DSA
+	imply CMD_EXTENSION
 
 config SH
 	bool "SuperH architecture"
diff --git a/arch/sandbox/dts/Makefile b/arch/sandbox/dts/Makefile
index d231dc2877..3e5dc67d53 100644
--- a/arch/sandbox/dts/Makefile
+++ b/arch/sandbox/dts/Makefile
@@ -6,6 +6,7 @@ else
 dtb-$(CONFIG_SANDBOX) += sandbox.dtb
 endif
 dtb-$(CONFIG_UT_DM) += test.dtb
+dtb-$(CONFIG_CMD_EXTENSION) += overlay0.dtbo overlay1.dtbo
 
 targets += $(dtb-y)
 
diff --git a/arch/sandbox/dts/overlay0.dts b/arch/sandbox/dts/overlay0.dts
new file mode 100644
index 0000000000..70c6cf77aa
--- /dev/null
+++ b/arch/sandbox/dts/overlay0.dts
@@ -0,0 +1,9 @@
+/dts-v1/;
+/plugin/;
+
+&{/buttons} {
+	btn3 {
+		gpios = <&gpio_a 5 0>;
+		label = "button3";
+	};
+};
diff --git a/arch/sandbox/dts/overlay1.dts b/arch/sandbox/dts/overlay1.dts
new file mode 100644
index 0000000000..51621b3110
--- /dev/null
+++ b/arch/sandbox/dts/overlay1.dts
@@ -0,0 +1,9 @@
+/dts-v1/;
+/plugin/;
+
+&{/buttons} {
+	btn4 {
+		gpios = <&gpio_a 5 0>;
+		label = "button4";
+	};
+};
diff --git a/board/sandbox/sandbox.c b/board/sandbox/sandbox.c
index 902b99ed50..dcd73451a3 100644
--- a/board/sandbox/sandbox.c
+++ b/board/sandbox/sandbox.c
@@ -14,6 +14,9 @@
 #include <asm/global_data.h>
 #include <asm/test.h>
 #include <asm/u-boot-sandbox.h>
+#include <malloc.h>
+
+#include <extension_board.h>
 
 /*
  * Pointer to initial global data area
@@ -79,6 +82,26 @@ int ft_board_setup(void *fdt, struct bd_info *bd)
 	return fdt_add_mem_rsv(fdt, 0x00d02000, 0x4000);
 }
 
+#ifdef CONFIG_CMD_EXTENSION
+int extension_board_scan(struct list_head *extension_list)
+{
+	struct extension *extension;
+	int i;
+
+	for (i = 0; i < 2; i++) {
+		extension = calloc(1, sizeof(struct extension));
+		snprintf(extension->overlay, sizeof(extension->overlay), "overlay%d.dtbo", i);
+		snprintf(extension->name, sizeof(extension->name), "extension board %d", i);
+		snprintf(extension->owner, sizeof(extension->owner), "sandbox");
+		snprintf(extension->version, sizeof(extension->version), "1.1");
+		snprintf(extension->other, sizeof(extension->other), "Fictionnal extension board");
+		list_add_tail(&extension->list, extension_list);
+	}
+
+	return i;
+}
+#endif
+
 #ifdef CONFIG_BOARD_LATE_INIT
 int board_late_init(void)
 {
diff --git a/test/py/tests/test_extension.py b/test/py/tests/test_extension.py
new file mode 100644
index 0000000000..267cf2ff27
--- /dev/null
+++ b/test/py/tests/test_extension.py
@@ -0,0 +1,53 @@
+# SPDX-License-Identifier:  GPL-2.0+
+# Copyright (c) 2020
+# Author: Kory Maincent <kory.maincent@bootlin.com>
+
+# Test U-Boot's "extension" commands.
+
+import os
+import pytest
+import u_boot_utils
+
+overlay_addr = 0x1000
+
+SANDBOX_DTB='arch/sandbox/dts/sandbox.dtb'
+OVERLAY_DIR='arch/sandbox/dts/'
+
+def load_dtb(u_boot_console):
+    u_boot_console.log.action('Loading devicetree to RAM...')
+    u_boot_console.run_command('host load hostfs - $fdt_addr_r %s' % (os.path.join(u_boot_console.config.build_dir, SANDBOX_DTB)))
+    u_boot_console.run_command('fdt addr $fdt_addr_r')
+
+@pytest.mark.buildconfigspec('cmd_fdt')
+@pytest.mark.boardspec('sandbox')
+def test_extension(u_boot_console):
+    """Test the 'extension' command."""
+
+    load_dtb(u_boot_console)
+
+    output = u_boot_console.run_command('extension list')
+    assert('No extension' in output)
+
+    output = u_boot_console.run_command('extension scan')
+    assert output == 'Found 2 extension board(s).'
+
+    output = u_boot_console.run_command('extension list')
+    assert('overlay0.dtbo' in output)
+    assert('overlay1.dtbo' in output)
+
+    u_boot_console.run_command_list([
+        'setenv extension_overlay_addr %s' % (overlay_addr),
+        'setenv extension_overlay_cmd \'host load hostfs - ${extension_overlay_addr} %s${extension_overlay_name}\'' % (os.path.join(u_boot_console.config.build_dir, OVERLAY_DIR))])
+
+    output = u_boot_console.run_command('extension apply 0')
+    assert('bytes read' in output)
+
+    output = u_boot_console.run_command('fdt print')
+    assert('button3' in output)
+
+    output = u_boot_console.run_command('extension apply all')
+    assert('bytes read' in output)
+
+    output = u_boot_console.run_command('fdt print')
+    assert('button4' in output)
+