diff --git a/tests/test.cmp b/tests/test.cmp
index aaa89f1b..1234ea26 100644
--- a/tests/test.cmp
+++ b/tests/test.cmp
@@ -16719,6 +16719,29 @@ mbpad("foo", "🙂💩", 3) => "foo"
 mbpad("foo", "🙂💩", 3, 1) => "foo"
 mbpad("foo", "🙂💩", 8) => "🙂💩🙂💩🙂foo"
 mbpad("foo", "🙂💩", 8, 1) => "foo🙂💩🙂💩🙂"
+char(255) => "ÿ"
+bad => "ÿ"
+mbpad("foo", "ÿ", 3) => "foo"
+bad => "ÿ"
+mbpad("foo", "ÿ", 3, 1) => "foo"
+bad => "ÿ"
+mbpad("foo", "ÿ", 8) => Invalid multibyte sequence
+../tests/test.rem(1869): mbpad(): Invalid multibyte sequence
+bad => "ÿ"
+mbpad("foo", "ÿ", 8, 1) => Invalid multibyte sequence
+../tests/test.rem(1870): mbpad(): Invalid multibyte sequence
+bad => "ÿ"
+mbpad("ÿ", "bar", 0) => Invalid multibyte sequence
+../tests/test.rem(1871): mbpad(): Invalid multibyte sequence
+bad => "ÿ"
+mbpad("ÿ", "bar", 0, 1) => Invalid multibyte sequence
+../tests/test.rem(1872): mbpad(): Invalid multibyte sequence
+bad => "ÿ"
+mbpad("ÿ", "bar", 8) => Invalid multibyte sequence
+../tests/test.rem(1873): mbpad(): Invalid multibyte sequence
+bad => "ÿ"
+mbpad("ÿ", "bar", 8, 1) => Invalid multibyte sequence
+../tests/test.rem(1874): mbpad(): Invalid multibyte sequence
 Variable hash table statistics:
   Entries: 100146; Buckets: 87719; Non-empty Buckets: 66303
   Maxlen: 5; Minlen: 0; Avglen: 1.142; Stddev: 0.878; Avg nonempty len: 1.510
@@ -16740,7 +16763,7 @@ Expression nodes high-water: 302076
     Expression nodes leaked: 0
      Parse level high-water: 34
 Max expr node evaluations per line: 2001
-Total expression node evaluations:  106643
+Total expression node evaluations:  106681
 
 Test 2
 
diff --git a/tests/test.rem b/tests/test.rem
index 0de6587c..87ce18ab 100644
--- a/tests/test.rem
+++ b/tests/test.rem
@@ -1863,6 +1863,16 @@ set a mbpad("foo", "🙂💩", 3)
 set a mbpad("foo", "🙂💩", 3, 1)
 set a mbpad("foo", "🙂💩", 8)
 set a mbpad("foo", "🙂💩", 8, 1)
+set bad char(255)
+set a mbpad("foo", bad, 3)
+set a mbpad("foo", bad, 3, 1)
+set a mbpad("foo", bad, 8)
+set a mbpad("foo", bad, 8, 1)
+set a mbpad(bad, "bar", 0)
+set a mbpad(bad, "bar", 0, 1)
+set a mbpad(bad, "bar", 8)
+set a mbpad(bad, "bar", 8, 1)
+
 DEBUG -x
 # Don't want Remind to queue reminders
 EXIT