diff --git a/test/004_missing_option_argument.txt b/test/004_missing_option_argument.txt
index fc34c96..d0fa894 100644
--- a/test/004_missing_option_argument.txt
+++ b/test/004_missing_option_argument.txt
@@ -3,6 +3,7 @@
 :INPUT
 :OUTPUT-FILTER
 1s/^.\+: /boxes: /
+1s/-- s$/-- 's'/
 :EXPECTED-ERROR 1
 boxes: option requires an argument -- 's'
 Usage: boxes [options] [infile [outfile]]
diff --git a/test/065_size_missing_argument.txt b/test/065_size_missing_argument.txt
index cb77672..2c432e7 100644
--- a/test/065_size_missing_argument.txt
+++ b/test/065_size_missing_argument.txt
@@ -4,6 +4,7 @@
 foo
 :OUTPUT-FILTER
 1s/^.\+: /boxes: /
+1s/-- s$/-- 's'/
 :EXPECTED-ERROR 1
 boxes: option requires an argument -- 's'
 Usage: boxes [options] [infile [outfile]]