diff --git a/tools/targets/__init__.py b/tools/targets/__init__.py
index ce5de16ecc..2225c34ac6 100644
--- a/tools/targets/__init__.py
+++ b/tools/targets/__init__.py
@@ -490,7 +490,7 @@ class MCU_NRF51Code(object):
             binh.merge(blh)
 
         with open(binf.replace(".bin", ".hex"), "w") as fileout:
-            binh.tofile(fileout, format='hex')
+            binh.write_hex_file(fileout, write_start_addr=False)
 
 class NCS36510TargetCode:
     @staticmethod