diff --git a/source/utf8/checked.h b/source/utf8/checked.h
index 1c1cadd..cc1ec47 100644
--- a/source/utf8/checked.h
+++ b/source/utf8/checked.h
@@ -109,13 +109,13 @@ namespace utf8
                 case internal::NOT_ENOUGH_ROOM:
                     throw not_enough_room();
                 case internal::INVALID_LEAD:
-                    utf8::append (replacement, out);
+                    out = utf8::append (replacement, out);
                     ++start;
                     break;
                 case internal::INCOMPLETE_SEQUENCE:
                 case internal::OVERLONG_SEQUENCE:
                 case internal::INVALID_CODE_POINT:
-                    utf8::append (replacement, out);
+                    out = utf8::append (replacement, out);
                     ++start;
                     // just one replacement mark for the sequence
                     while (start != end && utf8::internal::is_trail(*start))
diff --git a/test_drivers/smoke_test/test.cpp b/test_drivers/smoke_test/test.cpp
index 9273da2..7489835 100644
--- a/test_drivers/smoke_test/test.cpp
+++ b/test_drivers/smoke_test/test.cpp
@@ -153,12 +153,12 @@ int main()
     
     //replace_invalid
     char invalid_sequence[] = "a\x80\xe0\xa0\xc0\xaf\xed\xa0\x80z";
-    vector<char> replace_invalid_result;
-    replace_invalid (invalid_sequence, invalid_sequence + sizeof(invalid_sequence), back_inserter(replace_invalid_result), '?');
+    vector<char> replace_invalid_result(50);
+    replace_invalid (invalid_sequence, invalid_sequence + sizeof(invalid_sequence), replace_invalid_result.begin(), '?');
     bvalid = is_valid(replace_invalid_result.begin(), replace_invalid_result.end());
     assert (bvalid);
     const char* fixed_invalid_sequence = "a????z";
-    assert (std::equal(replace_invalid_result.begin(), replace_invalid_result.end(), fixed_invalid_sequence));
+    assert (std::equal(replace_invalid_result.begin(), replace_invalid_result.begin() + sizeof(fixed_invalid_sequence), fixed_invalid_sequence));
 
     // iterator
     utf8::iterator<const char*> it(threechars, threechars, threechars + 9);