diff --git a/ChangeLog b/ChangeLog
index 92d7977e0..13827accd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 2.x.x branch released xxxx-xx-xx
+
+Bugfix
+   * Fixed potential arithmetic overflow in mbedtls_base64_decode() that could
+     cause buffer bound checks to be bypassed. Found by Eyal Itkin.
+
 = mbed TLS 2.1.6 branch released 2016-10-17
 
 Security
diff --git a/library/base64.c b/library/base64.c
index 3432e5fcd..d4fdf6e1a 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -192,7 +192,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
         return( 0 );
     }
 
-    n = ( ( n * 6 ) + 7 ) >> 3;
+    n = ( 6 * ( n >> 3 ) ) + ( ( 6 * ( n & 0x7 ) + 7 ) >> 3 );
     n -= j;
 
     if( dst == NULL || dlen < n )