diff --git a/netwerk/streamconv/converters/nsBinHexDecoder.cpp b/netwerk/streamconv/converters/nsBinHexDecoder.cpp
--- a/netwerk/streamconv/converters/nsBinHexDecoder.cpp
+++ b/netwerk/streamconv/converters/nsBinHexDecoder.cpp
@@ -197,20 +197,24 @@ nsresult nsBinHexDecoder::ProcessNextSta
   /* handle state */
   switch (mState)
   {
     case BINHEX_STATE_START:
       mState = BINHEX_STATE_FNAME;
       mCount = 0;
 
       // c & 63 returns the length of mName. So if we need the length, that's how
       // you can figure it out....
       mName.SetLength(c & 63);
+      if (mName.Length() != c & 63) {
+        /* XXX ProcessNextState/ProcessNextChunk aren't rv checked */
+        mState = BINHEX_STATE_DONE;
+      }
       break;
 
     case BINHEX_STATE_FNAME:
       mName.BeginWriting()[mCount] = c;
 
       if (++mCount > mName.Length())
       {
         // okay we've figured out the file name....set the content type on the channel
         // based on the file name AND issue our delayed on start request....