diff --git a/infra/specs/PRESUBMIT.py b/infra/specs/PRESUBMIT.py
index f064cacaf8..0886ee6682 100644
--- a/infra/specs/PRESUBMIT.py
+++ b/infra/specs/PRESUBMIT.py
@@ -8,6 +8,7 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+import difflib
 import os
 import shlex
 
@@ -15,26 +16,37 @@ import shlex
 USE_PYTHON3 = True
 
 
-def _HasLocalChanges(input_api):
-  ret = input_api.subprocess.call(['git', 'diff', '--quiet'])
-  return ret != 0
-
-
 def CheckPatchFormatted(input_api, output_api):
   results = []
   file_filter = lambda x: x.LocalPath().endswith('.pyl')
-  affected_files = input_api.AffectedFiles(include_deletes=False,
-                                           file_filter=file_filter)
+  affected_files = input_api.AffectedFiles(
+      include_deletes=False, file_filter=file_filter
+  )
 
+  diffs = []
   for f in affected_files:
+    # NewContents just reads the file.
+    prev_content = f.NewContents()
+
     cmd = ['yapf', '-i', f.AbsoluteLocalPath()]
     if input_api.subprocess.call(cmd):
       results.append(
-          output_api.PresubmitError('Error calling "' + shlex.join(cmd) + '"'))
+          output_api.PresubmitError('Error calling "' + shlex.join(cmd) + '"')
+      )
 
-  if _HasLocalChanges(input_api):
-    msg = ('Diff found after running "yapf -i" on modified .pyl files.\n'
-           'Please commit or discard the new changes.')
+    new_content = f.NewContents()
+    if new_content != prev_content:
+      path = f.LocalPath()
+      diff = difflib.unified_diff(prev_content, new_content, path, path)
+      diffs.append(''.join(diff))
+
+  if diffs:
+    combined_diffs = '\n'.join(diffs)
+    msg = (
+        'Diff found after running "yapf -i" on modified .pyl files:\n'
+        f'{combined_diffs}\n'
+        'Please commit or discard the new changes.'
+    )
     results.append(output_api.PresubmitError(msg))
 
   return results