diff --git a/include/polarssl/base64.h b/include/polarssl/base64.h
index fb0d753a2..d04149344 100644
--- a/include/polarssl/base64.h
+++ b/include/polarssl/base64.h
@@ -3,7 +3,7 @@
  *
  * \brief RFC 1521 base64 encoding/decoding
  *
- *  Copyright (C) 2006-2010, Brainspark B.V.
+ *  Copyright (C) 2006-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
@@ -57,7 +57,7 @@ int base64_encode( unsigned char *dst, size_t *dlen,
 /**
  * \brief          Decode a base64-formatted buffer
  *
- * \param dst      destination buffer
+ * \param dst      destination buffer (can be NULL for checking size)
  * \param dlen     size of the buffer
  * \param src      source buffer
  * \param slen     amount of data to be decoded
@@ -67,8 +67,8 @@ int base64_encode( unsigned char *dst, size_t *dlen,
  *                 not correct. *dlen is always updated to reflect the amount
  *                 of data that has (or would have) been written.
  *
- * \note           Call this function with *dlen = 0 to obtain the
- *                 required buffer size in *dlen
+ * \note           Call this function with *dst = NULL or *dlen = 0 to obtain
+ *                 the required buffer size in *dlen
  */
 int base64_decode( unsigned char *dst, size_t *dlen,
                    const unsigned char *src, size_t slen );
diff --git a/library/base64.c b/library/base64.c
index 06305bb5e..4b823b297 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -1,7 +1,7 @@
 /*
  *  RFC 1521 base64 encoding/decoding
  *
- *  Copyright (C) 2006-2010, Brainspark B.V.
+ *  Copyright (C) 2006-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
@@ -163,7 +163,7 @@ int base64_decode( unsigned char *dst, size_t *dlen,
 
     n = ((n * 6) + 7) >> 3;
 
-    if( *dlen < n )
+    if( dst == NULL || *dlen < n )
     {
         *dlen = n;
         return( POLARSSL_ERR_BASE64_BUFFER_TOO_SMALL );