diff --git a/ChangeLog b/ChangeLog
index 8f0e8c1c7947..22d7dd49149c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.xx.x branch released xxxx-xx-xx
+
+Bugfix
+   * Fix private key DER output in the key_app_writer example. File contents
+     were shifted by one byte, creating an invalid ASN.1 tag. Fixed by
+     Christian Walther in #2239.
+
 = mbed TLS 2.14.0 branch released 2018-11-19
 
 Security
diff --git a/programs/pkey/key_app_writer.c b/programs/pkey/key_app_writer.c
index 13602c2e530f..ebf6ad134bec 100644
--- a/programs/pkey/key_app_writer.c
+++ b/programs/pkey/key_app_writer.c
@@ -173,7 +173,7 @@ static int write_private_key( mbedtls_pk_context *key, const char *output_file )
             return( ret );
 
         len = ret;
-        c = output_buf + sizeof(output_buf) - len - 1;
+        c = output_buf + sizeof(output_buf) - len;
     }
 
     if( ( f = fopen( output_file, "w" ) ) == NULL )