diff --git a/scripts/west_commands/sign.py b/scripts/west_commands/sign.py
index 7e3ef56c00a..b20e6948b96 100644
--- a/scripts/west_commands/sign.py
+++ b/scripts/west_commands/sign.py
@@ -172,7 +172,7 @@ class ImgtoolSigner(Signer):
     def sign_cmd(self, args, bcfg, infile, outfile):
         align = str(bcfg['FLASH_WRITE_BLOCK_SIZE'])
         vtoff = str(bcfg['CONFIG_TEXT_SECTION_OFFSET'])
-        slot_size = str(bcfg['FLASH_AREA_IMAGE_0_SIZE'])
+        slot_size = str(bcfg['DT_FLASH_AREA_IMAGE_0_SIZE'])
 
         sign_command = [args.tool_path or 'imgtool',
                         'sign',