diff --git a/gui.c b/gui.c
index 023714c..ba84fa7 100644
--- a/gui.c
+++ b/gui.c
@@ -35,13 +35,11 @@ static mu_Context *ctx = NULL;
 static int running = 1;
 
 /* engine state */
-static jack_client_t *client = NULL;
+static Engine *g_engine = NULL;
 static int active = 0;
 static float bpm = 120.0f;
 static int loop_length = 8;          /* beats */
 static int current_beat = 0;
-static float *buffer = NULL;
-static int buffer_size = 0;
 
 /* ---------------------------------------------------------------------------
  *  drawing helpers (stubs for microui)
@@ -68,9 +66,9 @@ static void gui_update(void)
         if (mu_button(ctx, active ? "Stop" : "Play")) {
             active = !active;
             if (active) {
-                engine_start(client);
+                engine_start(g_engine);
             } else {
-                engine_stop(client);
+                engine_stop(g_engine);
             }
         }
         if (mu_button(ctx, "Reset")) {
@@ -84,14 +82,14 @@ static void gui_update(void)
         mu_layout_row(ctx, 2, (int[]) { 60, -1 }, 0);
         mu_label(ctx, "BPM:");
         if (mu_slider(ctx, &bpm, 20.0f, 300.0f, 0, "%.0f", 0)) {
-            engine_set_bpm(client, bpm);
+            engine_set_bpm(g_engine, bpm);
         }
 
         /* loop length */
         mu_layout_row(ctx, 2, (int[]) { 60, -1 }, 0);
         mu_label(ctx, "Length:");
         if (mu_slider(ctx, (float*)&loop_length, 1.0f, 64.0f, 0, "%.0f", 0)) {
-            engine_set_loop_length(client, loop_length);
+            engine_set_loop_length(g_engine, loop_length);
         }
 
         /* beat indicator */
@@ -124,11 +122,9 @@ static void gui_update(void)
 /* ---------------------------------------------------------------------------
  *  main loop
  * ------------------------------------------------------------------------- */
-int gui_main(jack_client_t *jack_client, float *audio_buffer, int buf_size)
+int gui_main(Engine *engine)
 {
-    client = jack_client;
-    buffer = audio_buffer;
-    buffer_size = buf_size;
+    g_engine = engine;
 
     /* initialise microui */
     ctx = malloc(sizeof(mu_Context));
@@ -186,7 +182,7 @@ int gui_main(jack_client_t *jack_client, float *audio_buffer, int buf_size)
         }
 
         /* update engine state */
-        current_beat = engine_get_current_beat(client);
+        current_beat = engine_get_current_beat(g_engine);
 
         /* render GUI */
         gui_update();
diff --git a/gui.h b/gui.h
index 8fb4063..3dbce9e 100644
--- a/gui.h
+++ b/gui.h
@@ -1,8 +1,8 @@
 #ifndef GUI_H
 #define GUI_H
 
-#include <jack/jack.h>
+#include "engine.h"
 
-int gui_main(jack_client_t *client, float *audio_buffer, int buf_size);
+int gui_main(Engine *engine);
 
 #endif /* GUI_H */
diff --git a/test_gui.c b/test_gui.c
index bb5f802..86cf2d4 100644
--- a/test_gui.c
+++ b/test_gui.c
@@ -45,7 +45,7 @@ int main(void)
     int ret = gui_main(client, buffer, buffer_size);
 
     /* cleanup */
-    engine_cleanup(client);
+    engine_cleanup(g_engine);
     free(buffer);
     jack_client_close(client);