diff --git a/src/common/string.cpp b/src/common/string.cpp
index 559bf3311f..3f8cfe19fd 100644
--- a/src/common/string.cpp
+++ b/src/common/string.cpp
@@ -290,11 +290,11 @@ void wxString::InitWith(const wxChar *psz, size_t nPos, size_t nLength)
 {
   Init();
 
-  wxASSERT( nPos <= wxStrlen(psz) );
-
   if ( nLength == wxSTRING_MAXLEN )
     nLength = wxStrlen(psz + nPos);
 
+  wxASSERT_MSG( nPos + nLength <= wxStrlen(psz), _T("index out of bounds") );
+
   STATISTICS_ADD(InitialLength, nLength);
 
   if ( nLength > 0 ) {