diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index c334dbc..8725d14 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -111,7 +111,7 @@
 
     /* Add context value */
     *p++ = (unsigned char)( clen & 0xFF );
-    if( ctx != NULL )
+    if( clen != 0 )
         memcpy( p, ctx, clen );
 
     /* Return total length to the caller.  */