diff --git a/src/common/convauto.cpp b/src/common/convauto.cpp
index 9f3be27802..8778295207 100644
--- a/src/common/convauto.cpp
+++ b/src/common/convauto.cpp
@@ -334,9 +334,12 @@ wxConvAuto::ToWChar(wchar_t *dst, size_t dstLen,
         // to the fall-back conversion in this case as it would prevent us from
         // decoding UTF-8 input when fed it byte by byte, as done by
         // wxTextInputStream, for example
-        // 2 extra bytes are needed for inputs that start with 1 or 2 null bytes
+        // up to 2 extra bytes are needed for inputs that start with null bytes
         // that look like the start of UTF-32BE BOM, but can be in UTF-8 too
-        if ( srcLen < 2 + m_conv->GetMaxCharLen() && wxIsUTF8Prefix(src, srcLen) )
+        size_t nNull = 0;
+        if ( srcLen != wxNO_LEN && srcLen >= 2 && !src[0] )
+            nNull = ( src[1]? 1 : 2 );
+        if ( srcLen < nNull + m_conv->GetMaxCharLen() && wxIsUTF8Prefix(src, srcLen) )
             return wxCONV_FAILED;
 
         // if the conversion failed but we didn't really detect anything and
diff --git a/tests/mbconv/convautotest.cpp b/tests/mbconv/convautotest.cpp
index 6eaa24b155..27839f93a5 100644
--- a/tests/mbconv/convautotest.cpp
+++ b/tests/mbconv/convautotest.cpp
@@ -47,6 +47,7 @@ private:
         CPPUNIT_TEST( UTF8NoBom );
         CPPUNIT_TEST( Fallback );
         CPPUNIT_TEST( FallbackMultibyte );
+        CPPUNIT_TEST( FallbackShort );
         CPPUNIT_TEST( StreamUTF8NoBOM );
         CPPUNIT_TEST( StreamUTF8 );
         CPPUNIT_TEST( StreamUTF16LE );
@@ -100,6 +101,7 @@ private:
     void UTF8NoBom();
     void Fallback();
     void FallbackMultibyte();
+    void FallbackShort();
 
     // test whether two lines of text are converted properly from a stream
     void TestTextStream(const char *src,
@@ -222,6 +224,13 @@ void ConvAutoTestCase::FallbackMultibyte()
 #endif
 }
 
+void ConvAutoTestCase::FallbackShort()
+{
+    TestFirstChar("\x61\x61\x61\xc4", 'a', 4,
+                  ConvState(wxBOM_None, wxFONTENCODING_ISO8859_5, true),
+                  wxFONTENCODING_ISO8859_5);
+}
+
 void ConvAutoTestCase::TestTextStream(const char *src,
                                       size_t srclength,
                                       const wxString& line1,