diff --git a/src/async.c b/src/async.c
index 78626bb0..4cc86ea4 100644
--- a/src/async.c
+++ b/src/async.c
@@ -54,7 +54,7 @@ coap_register_async(coap_session_t *session,
     size_t i;
     char outbuf[2*8 + 1];
     size_t outbuflen;
-    
+
     outbuf[0] = '\000';
     for (i = 0; i < request->token_length; i++) {
       outbuflen = strlen(outbuf);