diff --git a/jack/port.h b/jack/port.h
index 9ee069d..796a19a 100644
--- a/jack/port.h
+++ b/jack/port.h
@@ -179,5 +179,8 @@ struct _jack_port {
 #define jack_output_port_buffer(p) \
   ((void *) (*(p)->client_segment_base + (p)->shared->offset))
 
+/* not for use by JACK applications */
+size_t jack_port_type_buffer_size (jack_port_type_info_t* port_type_info, jack_nframes_t nframes);
+
 #endif /* __jack_port_h__ */
 
diff --git a/jackd/engine.c b/jackd/engine.c
index 4876653..677d993 100644
--- a/jackd/engine.c
+++ b/jackd/engine.c
@@ -438,14 +438,7 @@ jack_resize_port_segment (jack_engine_t *engine,
 	jack_port_type_info_t* port_type = &engine->control->port_types[ptid];
 	jack_shm_info_t* shm_info = &engine->port_segment[ptid];
 
-	if (port_type->buffer_scale_factor < 0) {
-		one_buffer = port_type->buffer_size;
-	} else {
-		one_buffer = sizeof (jack_default_audio_sample_t)
-			* port_type->buffer_scale_factor
-			* engine->control->buffer_size;
-	}
-
+	one_buffer = jack_port_type_buffer_size (port_type, engine->control->buffer_size);
 	VERBOSE (engine, "resizing port buffer segment for type %d, one buffer = %u bytes", ptid, one_buffer);
 
 	size = nports * one_buffer;
diff --git a/libjack/port.c b/libjack/port.c
index 7865c91..de8304e 100644
--- a/libjack/port.c
+++ b/libjack/port.c
@@ -559,15 +559,7 @@ jack_port_get_buffer (jack_port_t *port, jack_nframes_t nframes)
 	   connection process.
 	*/
 	if (port->mix_buffer == NULL) {
-		size_t buffer_size;
-		if( port->type_info->buffer_scale_factor < 0 ) {
-			buffer_size = port->type_info->buffer_size;
-		} else {
-			buffer_size = 
-				port->type_info->buffer_scale_factor
-				* sizeof (jack_default_audio_sample_t)
-				* nframes;
-		}
+		size_t buffer_size = jack_port_type_buffer_size (port->type_info, nframes);
 		port->mix_buffer = jack_pool_alloc (buffer_size);
 		port->fptr.buffer_init (port->mix_buffer, buffer_size, nframes);
 	}
@@ -575,6 +567,17 @@ jack_port_get_buffer (jack_port_t *port, jack_nframes_t nframes)
 	return (void *) port->mix_buffer;
 }
 
+size_t
+jack_port_type_buffer_size (jack_port_type_info_t* port_type_info, jack_nframes_t nframes)
+{
+	if( port_type_info->buffer_scale_factor < 0 ) {
+		return port_type_info->buffer_size;
+	} 
+
+	return port_type_info->buffer_scale_factor
+		* sizeof (jack_default_audio_sample_t)
+		* nframes;
+}
 int
 jack_port_tie (jack_port_t *src, jack_port_t *dst)