diff --git a/src/common/string.cpp b/src/common/string.cpp
index 395a09476c..3ca72d8e68 100644
--- a/src/common/string.cpp
+++ b/src/common/string.cpp
@@ -229,24 +229,37 @@ wxString::wxString(const void *pStart, const void *pEnd)
 // from multibyte string
 wxString::wxString(const char *psz, wxMBConv& conv, size_t nLength)
 {
-  // first get necessary size
-  size_t nLen = psz ? conv.MB2WC((wchar_t *) NULL, psz, 0) : 0;
-
-  // nLength is number of *Unicode* characters here!
-  if ((nLen != (size_t)-1) && (nLen > nLength))
-    nLen = nLength;
-
-  // empty?
-  if ( (nLen != 0) && (nLen != (size_t)-1) ) {
-    if ( !AllocBuffer(nLen) ) {
-      wxFAIL_MSG( _T("out of memory in wxString::wxString") );
-      return;
+    // first get the size of the buffer we need
+    size_t nLen;
+    if ( psz )
+    {
+        // calculate the needed size ourselves or use a provide one
+        nLen = nLength == wxSTRING_MAXLEN ? conv.MB2WC(NULL, psz, 0) : nLength;
     }
-    conv.MB2WC(m_pchData, psz, nLen);
-  }
-  else {
+    else
+    {
+        // nothing to convert
+        nLen = 0;
+    }
+
+    // anything to do?
+    if ( (nLen != 0) && (nLen != (size_t)-1) )
+    {
+        if ( !AllocBuffer(nLen) )
+        {
+            wxFAIL_MSG( _T("out of memory in wxString::wxString") );
+            return;
+        }
+
+        if ( conv.MB2WC(m_pchData, psz, nLen) != (size_t)-1 )
+        {
+            // initialized ok
+            return;
+        }
+        //else: the conversion failed -- leave the string empty (what else?)
+    }
+
     Init();
-  }
 }
 
 #else // ANSI
@@ -255,27 +268,37 @@ wxString::wxString(const char *psz, wxMBConv& conv, size_t nLength)
 // from wide string
 wxString::wxString(const wchar_t *pwz, wxMBConv& conv, size_t nLength)
 {
-  // first get necessary size
-  size_t nLen = 0;
-  if (pwz)
-  {
-    if (nLength == wxSTRING_MAXLEN)
-      nLen = conv.WC2MB((char *) NULL, pwz, 0);
-    else
-      nLen = nLength;
-  }
-
-  // empty?
-  if ( (nLen != 0) && (nLen != (size_t)-1) ) {
-    if ( !AllocBuffer(nLen) ) {
-      wxFAIL_MSG( _T("out of memory in wxString::wxString") );
-      return;
+    // first get the size of the buffer we need
+    size_t nLen;
+    if ( pwz )
+    {
+        // calculate the needed size ourselves or use a provide one
+        nLen = nLength == wxSTRING_MAXLEN ? conv.WC2MB(NULL, pwz, 0) : nLength;
     }
-    conv.WC2MB(m_pchData, pwz, nLen);
-  }
-  else {
+    else
+    {
+        // nothing to convert
+        nLen = 0;
+    }
+
+    // anything to do?
+    if ( (nLen != 0) && (nLen != (size_t)-1) )
+    {
+        if ( !AllocBuffer(nLen) )
+        {
+            wxFAIL_MSG( _T("out of memory in wxString::wxString") );
+            return;
+        }
+
+        if ( conv.WC2MB(m_pchData, pwz, nLen) != (size_t)-1 )
+        {
+            // initialized ok
+            return;
+        }
+        //else: the conversion failed -- leave the string empty (what else?)
+    }
+
     Init();
-  }
 }
 #endif // wxUSE_WCHAR_T