diff --git a/ChangeLog b/ChangeLog
index 2da6a2a..b61c2c5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 1.3.13 reladsed 2015-??-??
+
+Bugfix
+   * Setting SSL_MIN_DHM_BYTES in config.h had no effect (overriden in ssl.h)
+     (found by Fabio Solari) (#256)
+
 = mbed TLS 1.3.12 released 2015-08-11
 
 Security
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 9c6a0c5..1f9f8be 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -287,7 +287,9 @@
  * The default is 1024 bits (128 bytes) for compatibility reasons.
  * From a purely security perspective, 2048 bits would be better.
  */
+#if !defined(SSL_MIN_DHM_BYTES)
 #define SSL_MIN_DHM_BYTES             128   /**< Min size of the Diffie-Hellman prime */
+#endif
 /* \} name SECTION: Module settings */
 
 /*