diff --git a/library/x509parse.c b/library/x509parse.c
index fff6dd6..ea59bec 100644
--- a/library/x509parse.c
+++ b/library/x509parse.c
@@ -1949,6 +1949,8 @@
     filename[len++] = '*';
 
 	w_ret = MultiByteToWideChar( CP_ACP, 0, filename, len, szDir, MAX_PATH - 3 );
+    if( w_ret == 0 )
+        return( POLARSSL_ERR_X509_INVALID_INPUT );
 
     hFind = FindFirstFileW( szDir, &file_data );
     if (hFind == INVALID_HANDLE_VALUE) 
@@ -1966,6 +1968,8 @@
 									 lstrlenW(file_data.cFileName),
 									 p, len - 1,
 									 NULL, NULL );
+        if( w_ret == 0 )
+            return( POLARSSL_ERR_X509_FILE_IO_ERROR );
 
         w_ret = x509parse_crtfile( chain, filename );
         if( w_ret < 0 )