diff --git a/library/x509_crt.c b/library/x509_crt.c
index f73e215..2ad051f 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1573,6 +1573,14 @@
     if (FAILED (SizeTToInt(len, &lengthAsInt)))
         return(MBEDTLS_ERR_X509_FILE_IO_ERROR);
 
+    /*
+     * Note this function uses the code page CP_ACP, and assumes the incoming
+     * string is encoded in ANSI, before translating it into Unicode. If the
+     * incoming string were changed to be UTF-8, then the length check needs to
+     * change to check the number of characters, not the number of bytes, in the
+     * incoming string are less than MAX_PATH to avoid a buffer overrun with
+     * MultiByteToWideChar().
+     */
     w_ret = MultiByteToWideChar(CP_ACP, 0, filename, (int) len, szDir,
                                 MAX_PATH - 3);
     if (w_ret == 0) {