diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index ea1d63e..1b1ba69 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -779,6 +779,12 @@
 
     SSL_DEBUG_MSG( 2, ( "=> write server hello" ) );
 
+    if( ssl->f_rng == NULL )
+    {
+        SSL_DEBUG_MSG( 1, ( "no RNG provided") );
+        return( POLARSSL_ERR_SSL_NO_RNG );
+    }
+
     /*
      *     0  .   0   handshake type
      *     1  .   3   handshake length