diff --git a/tools/config/__init__.py b/tools/config/__init__.py
index 3d98a15d49..f1de54e020 100644
--- a/tools/config/__init__.py
+++ b/tools/config/__init__.py
@@ -545,11 +545,11 @@ class Config(object):
                 rom_start = int(cmsis_part['memory']['PROGRAM_FLASH']['start'], 0)
             except KeyError:
                 raise ConfigException("Not enough information in CMSIS packs to "
-                                  "build a bootloader project")
+                                      "build a bootloader project")
         if  ('target.bootloader_img' in target_overrides or
              'target.restrict_size' in target_overrides):
             return self._generate_bootloader_build(target_overrides,
-                                                  rom_start, rom_size)
+                                                   rom_start, rom_size)
         elif ('target.mbed_app_start' in target_overrides or
               'target.mbed_app_size' in target_overrides):
             return self._generate_linker_overrides(target_overrides,
@@ -559,7 +559,7 @@ class Config(object):
                 "Bootloader build requested but no bootlader configuration")
 
     def _generate_bootloader_build(self, target_overrides, rom_start, rom_size):
-        start = 0
+        start = rom_start
         if 'target.bootloader_img' in target_overrides:
             basedir = abspath(dirname(self.app_config_location))
             filename = join(basedir, target_overrides['target.bootloader_img'])
@@ -579,7 +579,7 @@ class Config(object):
             new_size = Config._align_floor(start + new_size, self.sectors) - start
             yield Region("application", start, new_size, True, None)
             start += new_size
-            yield Region("post_application", rom_start + start, rom_size - start,
+            yield Region("post_application", start, rom_size - start,
                          False, None)
         else:
             yield Region("application", start, rom_size - start,