diff --git a/ion/test/utf8_decoder.cpp b/ion/test/utf8_decoder.cpp
index 56e280fa4..26248502a 100644
--- a/ion/test/utf8_decoder.cpp
+++ b/ion/test/utf8_decoder.cpp
@@ -7,9 +7,21 @@ void assert_decodes_to(const char * string, CodePoint c) {
   quiz_assert(d.nextCodePoint() == 0);
 }
 
-QUIZ_CASE(ion_utf8_decoder) {
+void assert_previous_code_point_is_to(const char * string, const char * stringPosition, CodePoint c) {
+  UTF8Decoder d(string, stringPosition);
+  quiz_assert(d.previousCodePoint() == c);
+}
+
+QUIZ_CASE(ion_utf8_decode_forward) {
   assert_decodes_to("\x20", 0x20);
   assert_decodes_to("\xC2\xA2", 0xA2);
   assert_decodes_to("\xED\x9F\xBF", 0xD7FF);
   assert_decodes_to("\xCC\x81", 0x301);
 }
+
+QUIZ_CASE(ion_utf8_decode_backwards) {
+  const char * a = "abcde";
+  assert_previous_code_point_is_to(a, a+1, *a);
+  assert_previous_code_point_is_to(a, a+4, *(a+3));
+  assert_previous_code_point_is_to(a, a+6, *(a+5));
+}