diff --git a/tests/backup-prefix-suffix b/tests/backup-prefix-suffix
index 27eab5b..d31f0b3 100644
--- a/tests/backup-prefix-suffix
+++ b/tests/backup-prefix-suffix
@@ -21,7 +21,7 @@ cat > ab.diff <<EOF
 EOF
 
 echo one > f
-check 'patch -b -p1 < ab.diff' <<EOF
+check 'patch --debug=4 -b -p1 < ab.diff' <<EOF
 patching file f
 EOF