diff --git a/t/t4008-diff-break-rewrite.sh b/t/t4008-diff-break-rewrite.sh
index 5836e3a899..1287d2ad17 100755
--- a/t/t4008-diff-break-rewrite.sh
+++ b/t/t4008-diff-break-rewrite.sh
@@ -119,7 +119,7 @@ test_expect_success \
     'compare_diff_raw expected current'
 
 test_expect_success \
-    'run diff with -B' \
+    'run diff with -B -M' \
     'git diff-index -B -M "$tree" >current'
 
 # This should not mistake file0 as the copy source of new file1