diff --git a/agent/command.c b/agent/command.c
index 3a547ffaa..f9bc6ca96 100644
--- a/agent/command.c
+++ b/agent/command.c
@@ -1031,7 +1031,8 @@ cmd_readkey (assuan_context_t ctx, char *line)
             rc = gpg_error_from_syserror ();
           else
             {
-              gcry_sexp_sprint (s_pkey, GCRYSEXP_FMT_CANON, pkbuf, pkbuflen);
+              pkbuflen = gcry_sexp_sprint (s_pkey, GCRYSEXP_FMT_CANON,
+                                           pkbuf, pkbuflen);
               rc = assuan_send_data (ctx, pkbuf, pkbuflen);
             }
         }