diff --git a/libcpp/charset.c b/libcpp/charset.c
index cba19a6..6d67bca 100644
--- a/libcpp/charset.c
+++ b/libcpp/charset.c
@@ -1731,7 +1731,10 @@ _cpp_convert_input (cpp_reader *pfile, const char *input_charset,
   /* Resize buffer if we allocated substantially too much, or if we
      haven't enough space for the \n-terminator.  */
   if (to.len + 4096 < to.asize || to.len >= to.asize)
-    to.text = XRESIZEVEC (uchar, to.text, to.len + 1);
+    {
+      to.text = XRESIZEVEC (uchar, to.text, to.len + 17);
+      memset (to.text + to.len + 1, 0, 16);
+    }
 
   /* If the file is using old-school Mac line endings (\r only),
      terminate with another \r, not an \n, so that we do not mistake