diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index 49d1f0a..13201ef 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -376,6 +376,40 @@
     return None
   return base_fs_file
 
+
+def CheckHeadroom(ext4fs_output, prop_dict):
+  """Checks if there's enough headroom space available.
+
+  Headroom is the reserved space on system image (via PRODUCT_SYSTEM_HEADROOM),
+  which is useful for devices with low disk space that have system image
+  variation between builds. The 'partition_headroom' in prop_dict is the size
+  in bytes, while the numbers in 'ext4fs_output' are for 4K-blocks.
+
+  Args:
+    ext4fs_output: The output string from mke2fs command.
+    prop_dict: The property dict.
+
+  Returns:
+    The check result.
+  """
+  ext4fs_stats = re.compile(
+      r'Created filesystem with .* (?P<used_blocks>[0-9]+)/'
+      r'(?P<total_blocks>[0-9]+) blocks')
+  m = ext4fs_stats.match(ext4fs_output.strip().split('\n')[-1])
+  used_blocks = int(m.groupdict().get('used_blocks'))
+  total_blocks = int(m.groupdict().get('total_blocks'))
+  headroom_blocks = int(prop_dict.get('partition_headroom')) / BLOCK_SIZE
+  adjusted_blocks = total_blocks - headroom_blocks
+  if used_blocks > adjusted_blocks:
+    mount_point = prop_dict.get("mount_point")
+    print("Error: Not enough room on %s (total: %d blocks, used: %d blocks, "
+          "headroom: %d blocks, available: %d blocks)" % (
+              mount_point, total_blocks, used_blocks, headroom_blocks,
+              adjusted_blocks))
+    return False
+  return True
+
+
 def BuildImage(in_dir, prop_dict, out_file, target_out=None):
   """Build an image to out_file from in_dir with property prop_dict.
 
@@ -532,7 +566,6 @@
     shutil.copytree(origin_in, staging_system, symlinks=True)
 
   ext4fs_output = None
-
   try:
     if fs_type.startswith("ext4"):
       (ext4fs_output, exit_code) = RunCommand(build_command)
@@ -550,24 +583,10 @@
     print("Error: '%s' failed with exit code %d" % (build_command, exit_code))
     return False
 
-  # Check if there's enough headroom space available. This is useful for devices
-  # with low disk space that have system image variation between builds.
+  # Check if there's enough headroom space available for ext4 image.
   if "partition_headroom" in prop_dict and fs_type.startswith("ext4"):
     assert ext4fs_output is not None
-    ext4fs_stats = re.compile(
-        r'Created filesystem with .* (?P<used_blocks>[0-9]+)/'
-        r'(?P<total_blocks>[0-9]+) blocks')
-    m = ext4fs_stats.match(ext4fs_output.strip().split('\n')[-1])
-    used_blocks = int(m.groupdict().get('used_blocks'))
-    total_blocks = int(m.groupdict().get('total_blocks'))
-    headroom_blocks = int(prop_dict.get('partition_headroom')) / BLOCK_SIZE
-    adjusted_blocks = total_blocks - headroom_blocks
-    if used_blocks > adjusted_blocks:
-      mount_point = prop_dict.get("mount_point")
-      print("Error: Not enough room on %s (total: %d blocks, used: %d blocks, "
-            "headroom: %d blocks, available: %d blocks)" % (
-                mount_point, total_blocks, used_blocks,
-                headroom_blocks, adjusted_blocks))
+    if not CheckHeadroom(ext4fs_output, prop_dict):
       return False
 
   if not fs_spans_partition: