diff --git a/tests/mbconv/mbconvtest.cpp b/tests/mbconv/mbconvtest.cpp
index 37abb9e5a9..8306759fb0 100644
--- a/tests/mbconv/mbconvtest.cpp
+++ b/tests/mbconv/mbconvtest.cpp
@@ -1147,7 +1147,7 @@ void MBConvTestCase::TestDecoder(
     // make sure the correct output length was calculated
     WX_ASSERT_EQUAL_MESSAGE
     (
-        ("while converting \"%s\"", multiBuffer),
+        ("while converting \"%s\"", inputCopy),
         wideChars,
         outputWritten
     );