diff --git a/g10/build-packet.c b/g10/build-packet.c
index 2e6dfc026..538f2fe13 100644
--- a/g10/build-packet.c
+++ b/g10/build-packet.c
@@ -220,7 +220,8 @@ write_fake_data (IOBUF out, gcry_mpi_t a)
       void *p;
 
       p = gcry_mpi_get_opaque ( a, &n );
-      iobuf_write (out, p, (n+7)/8 );
+      if (p)
+        iobuf_write (out, p, (n+7)/8 );
     }
 }